The H-53: An Air Force Pilot's Perspective
The operational characteristics of the H-53's assigned to the 21st SOS and 40th ARRS were major determinants of the way in which the Mayaguez-Koh Tang operation was planned. Their flight and maintenance characteristics played a key role in determining the outcome—or rather in establishing the range of possible outcomes—for the battle hinged on a number of highly improbable events. If there was a single, unavoidable, critical path in planning and execution, it was the capabilities and limitations of the CH- and HH-53's that transported the American Marines to their objectives and got them back. Several factors combined to make that path as critical as it was, not all of them readily quantifiable.
The first of these was the small number of H-53's available, a straightforward numerical consideration. The second factor was maintainability and in-commission rates; of those available, how many could be brought into commission when they were needed, how quickly, and with what degree of assurance. Although less readily quantifiable than the first factor, this, too, can be addressed in numerical terms. Here we are concerned with the qualitative factors involved in keeping the H-53 in safe flying condition. The third factor was the basic performance parameters that determined what the aircraft could do operationally, parameters that owed much to the H-53's Marine Corps origins. We have addressed these in gross quantitative terms, but there is more to operational effectiveness than speed, payload, range, and the tradeoffs among them. Some key factors, like maneuverability, are not readily quantified—not least of all because they are dependent upon aircrew skill, motivation, and knowledge. Many of the critical determinants of aircraft performance affecting combat effectiveness are heavily dependent on human factors and shade off into the subjective. It is those we are primarily concerned with here. What was the H-53 like to fly? What was it like to maintain? How much confidence did the crews have in it?
I do not pretend that my assessment of the H-53 as procured, maintained, and operated by the U.S. Air Force during the Southeast Asia conflict is definitive and unbiased. What I have to say here reflects my reaction to the machine as a pilot. As such, it is based on personal opinion. But what I have to say also reflects the information available to the men who flew in the Mayaguez-Koh Tang operation. There are matters on which honest men can differ, and I have tried to point these out. One point should be made clear up front: I am not concerned with the H-53 as procured, maintained, and flown by the Navy and Marine Corps. The Air Force H-53 was a very different kettle of fish.
The H-53 entered the Air Force inventory through a peculiar chain of circumstances that left an indelible imprint on the aircraft. Designed by Sikorsky Aircraft Company in response to a March 1961 Marine Corps request for proposal, the H-53 was a progressive development of the earlier piston-engined HR2S.1 The HR2S originated from the findings of a 1946 Marine Corps requirements board that called for a helicopter with a five-thousand-pound payload to support amphibious assault operations. By the standards of the day, the payload requirement was enormous—in 1946 most helicopters could carry little more than a pilot and passenger—and the H-53's exceptional performance was a direct result of that far-sighted requirement.
By specifying their operational needs ambitiously but in general terms, the Marines got a superior machine. There is, I believe, a lesson here, for the track record of U.S. military aircraft designed through tightly defined specifications rigorously justified by cost-benefit effectiveness has been less than sterling. The TFX/F-111 is the prime example, although the B-1B and a host of lesser programs might be cited as well.2 It is worth observing in passing the situation with the V-22 Osprey tilt-rotor vertical takeoff and landing assault transport. This machine has encountered opposition, in no small measure because the ambitious Marine Corps requirement around which it was designed is difficult to justify through cost-benefit comparisons that are implicitly based on the performance of existing systems.
Defining the requirement for a heavy-lift helicopter was only the first step. In the fiscally austere post-World War II defense environment, action in response to the board's finding was slow. But in March 1951, Sikorsky was awarded a developmental contract, winning out over competing designs by Piasecki and McDonnell.3 The HR2S was a capable machine, limited by the complexity of its twin R-2800 piston engine installation. It had the standard Sikorsky configuration, with a single lifting rotor and an antitorque tail rotor. The main rotor was fully articulated that is, each blade moved independently in the vertical and horizontal planes and was controllable in pitch. The main rotor blade spars were monolithic aluminum extrusions. Except for the engines, it looked a lot like the H-53.
Nor was the resemblance coincidental. The H-53 owed a great deal to the HR2S. The power train was an evolutionary development of that of the HR2S; the main rotor had the same seventy-two-foot diameter, but with six blades instead of five, and the four-bladed tail rotor was of similar design and dimensions.4 The key difference was the replacement of the HR2S's R-2800s with General Electric T-64 turbines. The adoption of turbine engines yielded enormous dividends, not only in speed and useful load but in mechanical simplicity and reliability.
The H-53 won a Navy-Marine design competition over a navalized version of the tandem-rotor Vertol CH-47 in the summer of 1962, and a production contract was let that September. Start-up, however, was delayed by fiscal strictures and by pressure from Secretary of Defense Robert McNamara to reconsider the Vertol proposal in the interests of interservice commonality. With Marine Corps encouragement, Sikorsky went back to the drawing board with a sharp pencil, cutting costs to the bone to win the contract. It is likely that the H-53's electrical system lost its battery at this point. Deliveries to operational units of the CH-53A, the first production version, did not begin until September 1966.5 When the CH-53A entered service, it was the biggest, fastest, and most capable military helicopter in the free world. With the sole exception of its three-engined CH-53E derivative, the CH-53A's C-, D-, and J-model descendants remain so today.6 The fact that the Marine Corps and our special operations forces are still dependent on so venerable an aircraft speaks volumes for the inadequacies of our defense procurement system.
Even before its birth as an independent service, the U.S. Air Force was ambivalent about helicopters. It is most unlikely that the Air Force would have procured high-performance rotary wing aircraft had it not been for the demands of the air war against North Vietnam. The stimulus was the need to rescue airmen shot down deep within enemy territory.7 When the Rolling Thunder campaign started in March 1965, the standard Air Force rescue helicopter was the Kaman HH-43B, designed as an aerial firefighting vehicle for noncombat local base rescue The H- 43's limited speed, range, and payload made it unsuitable for long-range combat missions, even in the later HH-43F version equipped with self-sealing fuel tanks and armor protection. Something more capable was needed quickly. Modified versions of the H-53 and the smaller H-3, an earlier Sikorsky product designed for the Navy as an antisubmarine platform and procured by the Air Force in modified form as the CH-3C, were the obvious candidates.
The Air Force approached Sikorsky with the problem. The H-3 came first, helped along by the fact that Sikorsky was already producing the CH-3C for the Air Force. The CH-3C was modified by adding jettisonable external fuel tanks mounted on stub wings extending from the sponsons, limited quarter-inch titanium armor-plate protection, an external hydraulic rescue hoist; a Doppler radar navigation system, a full radio communications suite including HF, VHF, VHF/FM, and UHF radios, and more powerful engines to compensate for the added weight.8 The result was the HH-3E, which began combat operations from bases in Thailand in October 1965. The HH-3E was an operational success, but the added weight stretched the design to its limits. The HH-3E was an interim solution that was still in service during Operation Desert Storm in the spring of 1991.
The HH-53 was to be the definitive long-range combat aircrew recovery helicopter. Procurement would take longer, however, because more extensive modifications were envisioned and because the Air Force would have to compete with the Marine Corps for space on the production line. Also, the Air Force had no preexisting contractual arrangements with Sikorsky for the H-53 design and procurement and was forced to deviate from normal procedures in the interest of time. In the meantime, Air Force engineers and test pilots at Wright-Patterson AFB, Ohio, demonstrated the feasibility of helicopter aerial refueling with the H-3. The HH-3E was retroactively fitted with a pneumatically extendible refueling probe, and by early 1967 operational crews were receiving air refueling training.9 The HH-53 was intended to be air-refuelable from the beginning.
Like the HH-3E, the HH-53 was fitted with jettisonable external tanks mounted on stub wings extending from the sponsons, an external hydraulic rescue hoist, quarter-inch titanium armor-plate protection for critical components, a pneumatically extendible refueling probe, a Doppler radar navigation system, and a full radio communications suite. In addition, the HH-53's power margin permitted significant defensive armament. That chosen was three Gatling-type, electrically driven, six-barreled 7.62-mm miniguns mounted in the crew door, in the left forward cabin window, and on the cargo ramp. From the standpoint of firepower and weight, the electrically driven minigun was not an obvious choice. It was heavy, its mechanism was mechanically complex, and, for reasons discussed below, it required its own independent electrical system.
Presumably, the choice was influenced by the minigun's successful use on the Air Force AC-47 gunship and the existence of contractual relationships with the manufacturer, General Electric. A .30-ca1./7.62 mm weapon with a high rate of fire was clearly preferable to a slower-firing weapon in the .50-ca1./12.7-mm category for suppressive use. But the minigun's maximum rate of four thousand rounds per minute was more than was needed. Crews almost always used the slower two thousand-round rate of fire to conserve ammunition and reduce the probability of jams. There were much lighter and simpler gas- and recoil-operated infantry machine guns extant with rates of fire exceeding twelve hundred rounds per minute, but they were apparently not considered—perhaps because they were not of American design.10
The first version was the HH-53B, an interim design with the external fuel tanks supported by struts pending redesign of the sponson. From the aircrew perspective, the HH-53B and HH-53C were virtually identical. The first two HH-53B's reached Udorn in August 1967, and six more were delivered before the arrival of the first HH-53C in September 1969.11 Like the HH-3E, the HH-53 was a success, sharing most of its predecessor's operational virtues and few of its vices. Tactical Air Command subsequently procured the H-53 for special operations but without aerial refueling or a ramp minigun.
The haste with which the American Air Force procured the H-53, though a remarkable achievement, created problems. All Air Force vehicles were required to have an independent, battery-driven backup electrical system to provide essential cockpit lighting and emergency instrumentation for instrument flight, typically a turn-and-slip indicator. The H-53 had no such system, in fact, outside of the minigun system it had no battery at all. The aircraft was started with a charge of compressed air that fired the APP (auxiliary power plant), a compact gas turbine mounted in the "dog house" above the cockpit and forward of the rotor head. The APP drove the generators, which provided electrical power for systems checkout and engine start. Once the engines were started, they drove the generators, and the APP was turned off. The arrangement may have made sense in achieving autonomy in the field, but if both generators failed under instrument conditions and you couldn't reset one of them immediately, you were a statistic. Like all single-rotor helicopters, the H-53 was inherently unstable.
Another apparent casualty of the irregular procurement program was the basic flight manual, or "dash one."12 The Air Force customarily purchased aircraft technical data from the manufacturer, but in the case of the H-53, the relevant manuals were written by civil service technical writers at Warner-Robins Air Material Center, Georgia. The official reason was presumably to save money. The real reason was apparently to preserve civil service jobs. The one thing certain was that the flight manual was poorly written. When I joined the H-53 community in 1974, much of the manual was written in language that was anything but clear. Many key passages were self-contradictory or simply wrong. Standardization submitted change request after change request, and over the years things gradually got better, but the pace was glacial. The problems were not fully ironed out until 1980-81.13
Probably the tech data that inspired the most complaints was that required for maintenance check flights, or functional check flights (FCFs), as they were called. Obtuse writing wasn't the only problem. Ordinarily, FCF checklists are expanded versions of the normal operations checklist, with the requisite maintenance checks superimposed on the normal checks. That way, there is only one checklist to run. In addition, FCF dash ones normally contain both the normal operating limits and the data needed to make the checks; for example, exhaust gas temperature as a function of density altitude and free air temperature for engine topping. With this setup, one crew member could run the FCF checklist and refer to the FCF dash one while the other two flew the airplane.
Not so with the H 53. The FCF checklist contained only the maintenance checks, so it was necessary to run the normal operations check list and the FCF checklist together. That required two sets of eyes. Also, the FCF flight manual did not contain normal operating limits, so many checks required reference to the normal dash one as well as the FCF manual. I have less-than-fond memories of FCFs for flight control rigging with the flight mechanic reading the FCF checklist, the copilot reading the normal operations checklist, the FCF dash one open in the copilot's lap, and the normal dash one open in my lap. Not only did the open flight manuals potentially impede flight control travel, but a good deal of self-discipline and attention were required to ensure that at least one crew member was looking outside at all times.
To make things even more interesting, certain FCF procedures were decidedly sporty. My favorites were the rigging checks for forward and aft cyclic control stick travel. These were made with the helicopter loaded to the maximum allowable longitudinal cg (center of gravity) limit, forward or aft depending on the check. To verify adequate aft stick travel, you loaded the helicopter to the maximum forward cg and hovered laterally to the right at the greatest allowable sideways speed of thirty-five knots (how you were supposed to know was unclear because there was no lateral airspeed indicator). The aircraft was therefore pushed to the limit in two performance criteria at once. Under those conditions, the nose of the aircraft would begin to tuck under. If you had enough aft stick travel to recover, the helicopter passed the check. What you were supposed to do if you did not, the FCF flight manual did not say. Vern Sheffield and I talked it over one day and decided that the best move would be to apply right rudder so you'd at least hit the ground going straight ahead.
The check for adequate forward stick travel was almost as bad; you loaded the helicopter to the aft cg limit and flew it to the maximum allowable forward speed in level flight. If you still had forward stick travel, the aircraft passed the check. At least you knew what your airspeed was, and if you ran out of stick travel, you could presumably recover by reducing power before the machine went out of control. H-53 units had special calibrated lead bars to load the aircraft to the cg limits. Lead is very dense, and by putting the bars at the extreme end of the cabin, you could get the desired cg with the minimum added weight. But if you got caught with a cyclic travel FCF away from home station, the only ready solution was to drive a flight-line tug into the cabin, park it, and tie it down in the appropriate position. That was less than ideal because flight-line tugs are extremely heavy, and the weight cut into your power margin. On one occasion, at Nellis AFB, Nevada, in the summer of 1978, I found myself facing not only the extreme airspeed and cg limits but maximum allowable gross weight for hovering under the prevailing conditions. If we had lost an engine during either check, we'd have had our hands full.
At bottom, the H-53 was an early 1960's upgrade of a 1950's design, and it showed its age in a number of areas. One was the vacuum-tube avionics, which were prone to unreliability until they warmed up, particularly under humid conditions. Another was the hundreds of fiber seals in the hydraulic system. Under pressure they would retain their integrity indefinitely, but when the aircraft was shut down, they cooled and shrank. When you cranked up again, there was a good chance that at least one seal would fail to reseat. When that happened, you had to find it, disconnect the line, replace it, and then reservice and bleed the affected system.
Hydraulics deserve particular attention, and the contrast between fixed-wing aircraft and helicopters is instructive. With fixed-wing aircraft, lift, thrust, and control of the aircraft in pitch, roll, and yaw are provided by essentially independent systems. If the engines fail, the ability of the wings to produce lift is not affected; similarly, a flight control malfunction affects thrust not at all and lift only indirectly.14 With a single-rotor helicopter, thrust, lift, and control are all provided by the main rotor, which controls the aircraft not only in pitch and roll but in speed and altitude as well. Without proper control inputs to the main rotor system, a helicopter is immediately and catastrophically unflyable. The nature and magnitude of the forces involved dictate that control by means of direct mechanical linkages is possible only with relatively small helicopters. The problem is compounded by the single lifting rotor/tail rotor configuration, which is inherently unstable about all three axes. This makes flight control fatiguing even with hydraulic boost. Gyroscopic stabilization systems that substitute electronic impulses for aerodynamic stability effectively solved the problem, but these, too, were dependent on hydraulics.
The H-53 had no fewer than three separate hydraulic systems, four counting the cargo winch system; the first- and second-stage flight control systems and the utility system, each with its own pumps, accumulators, and reservoirs. The design was conservative, and there were backups within backups—a Sikorsky hallmark—but they were complicated and not easily learned. The point is made by tracing the path of flight control inputs through the system Two reference gyros provided attitude information for the pilot's and copilot's attitude indicators and for the two AFCS (automatic flight control stabilization) systems, 1 and 2. Either of the two AFCS systems was capable of providing stabilization in pitch and roll independently, but normally they worked in parallel, combining and averaging their outputs. The AFCS units combined cyclic stick-control inputs with attitude information from the reference gyros to produce discrete signals in pitch and roll for the corresponding AFCS servos.
Control inputs from the collective pitch lever, rudder pedals, and a lateral accelerometer drove the altitude and yaw AFCS servos. Outputs from the four AFCS servos went into a mechanical mixing unit that translated discrete pitch, roll, yaw and collective signals into commands to the three primary flight control servos and the tail rotor servo. The primary flight control servos provided control in pitch, roll, power, and rotor RPM by changing the angular orientation and vertical position of a stationary swashplate beneath the main rotor head. This swashplate was set inside a rotating swashplate, which controlled the cyclic and collective pitch of the main rotor blades by means of pitch links that transmitted control inputs to the blades. The tail rotor servo provided control in yaw by changing the collective pitch of the tail rotor by means of a stationary and rotating swashplate and pitch link assembly. If all of this sounds complicated, make no mistake; it was.
After the above preamble, it will come as no surprise that many crew members found the H-53's flight control system complex and difficult to understand. Many were uncomfortable with it. The essentials were as follows: the primary flight control and the tail rotor servos were two-stage units, designed to maintain control with either stage should the other suffer hydraulic failure or internal mechanical failure or be shut down. The same was true of the pitch and roll AFCS servos. The first stages of the primary flight control and tail rotor servos were driven by the first-stage hydraulic system, which performed no other function. The second-stage hydraulic system drove the second stages of the primary flight control servos and provided pressure for AFCS 1, that is, for the first stages of the AFCS pitch and roll servos and for the AFCS yaw and altitude servos. The utility hydraulic system drove the second stage of the tail rotor servo and provided pressure for AFCS 2; that is, for the second stages of the AFCS pitch and roll servos. The first-stage hydraulic pump was driven by the main rotor system, providing for flight control hydraulic pressure in autorotation in the event of complete power failure. The second-stage and utility pumps were driven either by the engines or by the APP.
You could maintain flight control with first-stage hydraulics alone, but without the AFCS you flew the aircraft by brute force. This was extremely fatiguing and took more than the normal quotient of skill, especially on instruments. AFCS-out flight was taught and practiced as an emergency procedure only. You could lose either second-stage or utility hydraulics and still fly normally, but if you lost first-stage and then lost either second-stage or utility, you were dead meat. The end would come immediately and catastrophically if you lost first- and second- stage. It would come more gradually, if not more gracefully, if you lost first-stage and utility. Either way you were a goner. It is only fair to add that I know of no verifiable instance in which these circumstances actually happened. I do know of a case where most of a Jolly Green crew bailed out needlessly because they thought they had lost flight control hydraulics.
There is, or used to be, an aphorism among Air Force pilots that no matter how much power the designer builds into the machine, headquarters will find a way to add enough "essential" equipment to make it overloaded and underpowered. All other helicopters I flew during my Air Force career shared that problem; it was the only real flaw of the HH-3E, the HH-53's predecessor in rescue service and a real pilot's machine that I loved dearly. The H-53 was different. It was actually overpowered, the only military helicopter I was aware of that could merit such a claim. During the summer of 1993, I spoke to Lt. Col. Rich Comer, commander of the 20th SOS during Operations Desert Shield and Desert Storm and Barry Walls's copilot as a young second lieutenant in the Koh Tang operation. He told me that the categorization still applied to the MH-53J, despite the addition of terrain avoidance radar and FLIR (forward-looking infrared). Once in a while we get something right.
Add the armor, add the drop tanks, add the miniguns and ammunition, add the refueling probe and internal plumbing, add an extra crew member or two for insurance, and those big, beautiful General Electric T-64 engines just kept on trucking. Under any conditions but the most extreme—100ºF (38ºC)-plus on an August afternoon in the high Nevada desert—you hit the main gearbox torque limits before you ran out of power.
Like all single-lifting rotor helicopters, the H-53's hover performance tailed off sharply at density altitudes above eight thousand feet or so. In any serious situation I ever encountered, however, the gearbox was the limiting factor. If you got into real trouble, you just kept pulling collective until you hit the transient torque limits or the problem went away. You might exceed the transient exhaust gas turbine temperature limits if you weren't smooth, but normally the problem went away first. Finesse helped; you could get into power settling, but that's another matter. In addition, the H-53 was astonishingly maneuverable, although the young pilots I flew with in 1974-75 were not trained to exploit that maneuverability. It was not as smooth on the controls as the H-3, nor was it as good an instrument platform. But once you learned its ways, the H-53 did whatever you asked it to do with little complaint. From the pilot's standpoint, the only inherent problems with the basic configuration were cockpit visibility—which was no more than adequate—and limited ground clearance for the tail rotor and rear fuselage when landing and in a hover.
The cockpit visibility problem was partly caused by the small size of the side cockpit windows. This had further adverse consequences because the side windows also served as the pilots' primary emergency exit. For a broad-shouldered man wearing a backpack parachute—which we did—it was a tight fit. Emergency egress from the cockpit was not the best, and a word on parachutes is in order as well. To the best of my knowledge, Jolly Greens and Knives were the only helicopter crews to routinely wear parachutes. We began doing so in 1965 because our penetration tactics involved overflying small-arms and heavy automatic weapons fire at altitudes of eight thousand feet or more. When necessary, we would also cut through the top of the engagement envelope of 37-mm antiaircraft guns at ten to eleven thousand feet, despite the lack of oxygen equipment.15
The combat helicopter pilot's normal response to heavy battle damage is to autorotate; descend with the engines disengaged from the rotor system to land as quickly as possible. But if you were hit by antiaircraft artillery at such altitudes, odds were that the aircraft would explode, disintegrate, or burn before you reached the ground—hence the parachutes. By regulation, chutes were required for flight exceeding eight thousand feet above ground level and when aerial refueling. The flight mechanics and pararescuemen normally removed them at other times, but cockpit clearances were tight, and taking off your chute in the cockpit was a real chore. Some pilots slipped out of their harnesses before descent (the parachute was your back cushion), but even that involved a lot of thrashing around near the flight controls. Most of us just left it on.
In reality, parachutes were of marginal utility to H-53 drivers. On several occasions, pararescuemen and flight mechanics successfully parachuted from a stricken Jolly Green while the pilots did not. I know of no case where the converse was true. If the pilots made it, everybody made it. In a grim way, our parachutes were a badge of honor.
The rear fuselage and tail rotor clearance problem resulted from the need to make the helicopter sufficiently compact to fit on a carrier hangar deck. The landing gear was short. If you touched down on level ground with a nose-up attitude of more than 9.5º, the tail skid beneath the tail would hit before the wheels of the main landing gear. The H-53 was rigged for minimum drag at optimum cruise speed, that is, with the main rotor tilted forward to produce thrust for cruise flight, the fuselage was level. As a result, the H-53 hovered in a left-wing-low, nose-high attitude. Consequently, landings from a hover were singularly ungraceful; left main, right main, nose gear, wham, wham, bam! Tail clearance was a problem even in normal operations on level ground and runways, let alone over trees and in rough terrain. The tail rotor itself was vulnerable at flare angles that were normal in other helicopters—that was the reason for the skid—and you had to be especially careful maneuvering close to the ground. You learned to live with these problems.
In the fall of 1973, when I learned I was going into the H-53, I called my old buddy Barry Kamhoot and asked him about it. Barry had checked me out in HH-3E's at Udorn in 1966 and was a good, thinking pilot with lots of experience in a wide range of helicopters, including the >53. He responded that the H-53 wasn't as nice to fly as the H-3 but that it was tough, had plenty of power, and was a typical Sikorsky product with lots of reserve. Barry hit the nail on the head. It was tough, as the Koh Tang operation documented all too well. And if it was not as light on the controls or as good an instrument platform as the H-3, it was highly maneuverable. This was a point that Sikorsky and the Marines made by rolling and looping one, filming the exercise, and circulating the film among H-53 units. Admittedly, the demonstration used a lightly loaded aircraft, but the H-53 really was maneuverable, as we discovered when we relearned the value of tactical approaches and got into air-to-air training with fighters in 1977-78. It turned out to be a considerably more difficult target for an attacking fighter than either the Huey or the H-3, and power was a key ingredient. Besides having a highly competitive roll rate, an H-53 could accelerate from 90 to 170 knots in little more time than it takes to tell about it. That complicated the fighter pilot's lead problem and reduced the number of firing passes he could make in a given time.
The H-53's power and maneuverability significantly reduced the adverse effects of most of the undesirable flight characteristics that helicopter pilots worry about. Power limitations were rarely a factor. In contrast to most other helicopters, you didn't constantly worry about conserving RPM during an approach. The main exceptions resulted from the H-53's high disk loading, that is, high gross weight as a function of the main rotor disk area. The high disk loading translated into high rotor downwash velocities. The downwash in a hover was capable of picking up sizable objects—rocks, branches, and debris—and throwing them up into the rotor system. With reasonable care, however, the problem was not particularly serious. This was so partly because the extruded aluminum rotor blade spars, which included the leading edge, were tough and partly because the engine intakes were protected by efficient engine air-particle separators, or EAPS. Designed to protect engine compressor and turbine blades from the abrasive effects of sand and grit, the EAPS provided perfect protection against foreign object damage (FOD). The performance penalty was a trivial 150-lb. weight and a 3 percent loss in engine power. We and the Knives always flew with EAPS installed.
The high disk loading also entailed high descent rates in autorotation, and the H-53 autorotated like a greased safe. The optimum glide ratio—distance covered in unpowered flight divided by altitude lost—was only 4.5:1.16 That is pretty steep, and it looked even steeper because visibility from the cockpit straight ahead and down was poor. It was steeper when you turned because you had to keep the nose down to prevent rotor RPM from bleeding off. Close-in turning autorotations could get you into some interesting attitudes, and practice autorotations required a fair amount of attention and finesse. They weren't particularly difficult, though, once you got the hang of it, and were excellent confidence-builders. Because of the poor cockpit visibility, you had to initiate your flare at the bottom based mainly on radar altimeter readings. Because of landing gear structural limitations and the tail rotor clearance problem, practice autorotations ended with a power recovery at 150 feet. In 1975, practice autorotations had been banned by Rescue Service on the twin premises that the chances of simultaneously losing both engines in normal operations were remote and that practice autorotations entailed appreciable risk. The logic was sound as far as it went, but—characteristically—excluded the risks of combat and the benefits of aircrew confidence.
Another problem where the H-53's power didn't help was power settling, a condition analogous to getting behind the power curve in a fixed-wing aircraft. You knew you were in power settling when you pulled up on the collective pitch lever—the stick in your left hand that controls power and vertical movement—and instead of slowing its rate of descent, the helicopter dropped out from under you. Power settling is a real heart-stopper, and those who have experienced it remember it vividly. In 1975, the experts hadn't decided what power settling was. To the best of my knowledge, they still haven't. There were at least three possibilities: the main rotor becoming imbedded in a self-created ring vortex; the main rotor blades thrashing through the air in a stalled condition, producing little or no lift in a manner analogous to cavitation, and a condition in which a rapid application of collective increases the demand for power more rapidly than the engines can accelerate to produce it.17
Power settling was fluky and unpredictable. It generally happened at low airspeeds, particularly during downwind approaches, and when hovering out of ground effect (the "ground cushion" encountered at altitudes equal to or less than the main rotor diameter). You got out of power settling by lowering collective to recover RPM or by pushing the nose down to gain airspeed. H-53 pilots got into power settling on occasion but usually managed to recover without serious incident. In 1975 we were well aware of the phenomenon and were concerned about it, mostly because we didn't understand it. The conventional wisdom was that you prevented power settling by avoiding low airspeed descents and downwind approaches out of ground effect. It seemed to work.
The H-53 tended to wallow in a hover if you didn't stay on top of it. Compared to the H-3, the controls were sloppy and took getting used to. But as far as sheer maneuverability—the capacity to make rapid and precisely controlled excursions in airspeed, pitch, roll, and yaw—it beat anything else I have ever flown.18 This was especially true with tactical approaches, low-altitude maneuvers designed to get the helicopter from high-speed flight to a hover or landing as quickly as possible. Tactical approaches pushed to the limit are maximum performance maneuvers, testing the capabilities of both helicopter and pilot. A brief discussion of them is a good way to illustrate the H-53's characteristics and capabilities. Also, the Air Force's handling of tactical approaches reveals the philosophy behind the training that its helicopter crews received.
Tactical approaches were a bone of contention between those in the Air Force who believed in the importance of realistic, combat-oriented training and those who believed that the avoidance of accidents was the crux of our existence. Tactical approaches were formally incorporated into the Rescue Combat Crew Training School curriculum in the summer of 1966, and for several years thereafter students received thorough training in them. In 1966-67 we devoted a minimum of three or four training sorties of an hour and a half each almost entirely to tactical approaches and rescue hoist operations. That enabled the good-to-average student to become proficient, at least to the point of knowing his own limitations. But in time, as successive wing and squadron commanders had to brief rescue and MAC safety officers on the measures they were taking to prevent accidents, the emphasis on tactical approaches diminished. By the time I went through H-53 upgrade in the spring of 1974, we were down to a single demonstration sortie. The student himself wasn't even required to attempt a tactical approach. My instructor on that sortie, a fine officer and an exceptionally competent pilot in every other regard, was distinctly uncomfortable with tactical approaches. He made the requisite approach with jaw clenched and white knuckles (or so I surmise, for we were wearing gloves). I found to my horror that I was a living repository of forgotten knowledge.
There were several kinds of tactical approach. They were all, however, based on the common-sense dictum that you want to spend as little time as possible at low altitude and airspeed on a combat insert or extraction. That is where you are most vulnerable to enemy fire, getting in and out quickly is a good way to extend your life expectancy. Under most circumstances you go in low in the final stages of the approach, taking advantage of whatever cover and concealment the terrain offers. You avoid gaining altitude, because that makes you visible over a wider area. You have to come to a stop, so the trick is to slow down as quickly as possible. The most basic tactical approach, and in my opinion the best, involves trading off airspeed for g forces in a tight turn. There are other ways to do it, notably, a side flare approach in which you throw the helicopter into uncoordinated flight using the drag produced by driving the fuselage laterally through the air to slow down. That works, and the technique was used by at least some of the Knives and Jolly Greens going into Koh Tang. Personally, however, I have never been comfortable with deliberately putting a helicopter into an extreme uncoordinated flight condition. The instruments don't tell you what you're doing, and the aircraft isn't designed to fly that way.
To understand how a turning tactical approach works, begin with an imaginary helicopter approaching its desired landing or hover spot at high speed. The normal way to begin an approach to a landing or hover is to flare; pulling the nose up while reducing collective pitch (that is, lowering the collective pitch lever to reduce power and the net, or collective, pitch on the main rotor blades). But if you flare while flying straight ahead at high speed, one of three things happens: you overspeed the rotor, you climb, or both—all tactically undesirable. The solution is to flare in a turn. Instead of climbing, you use the g forces generated by the turn to absorb the additional collective pitch needed to keep the rotor from overspeeding. You could pull up to 3.5 g's in the H-53 without exceeding the airframe limits, so you had plenty to work with.
From the H-53 pilot's standpoint, a typical tactical approach begins with a high-speed pass (120 knots indicated airspeed was typical for training, but it could be faster, up to the red-line speed of 170 knots) over the landing or hover point. This allows the flight mechanic to look down and confirm that there really is a survivor on the ground or that the LZ is clear. On receiving confirmation, you roll into a level turn, typically of 60º bank or more, initially reducing collective pitch slightly to prevent the onset of g forces from bleeding off RPM. You will have worked out in advance the amount and direction of turn depending on topography, wind, and tactical considerations. If possible, the final approach will be into the wind to save time and maximize tail rotor clearance. Any combination can work, the only essential ingredient is a coordinated turn to reduce airspeed.
In my experience, the fastest approach involved a quartering downwind pass over your spot followed by a buttonhook turn of 235º or so into the wind. That was best only by a narrow margin. 270º turns, or even 360ºs, begun before you overflew your spot or with a short extension on downwind, worked fine. Once you had mastered the basic skills, tactical approaches were a very flexible and adaptable device. Note, too, that they were dependent on crew coordination as well as piloting skill, particularly in combat. Almost without exception, you were talked in on the final approach by the flight mechanic leaning out of the crew door. Clearances were frequently tight over rough terrain and trees, door, window, and ramp scanners served as your eyes.
Once established in the turn, you smoothly but aggressively apply back pressure on the cyclic. That raises the nose and, as in a straight ahead flare, forces airflow up through the main rotor system, increasing RPM. You counter the rise in RPM by increasing collective pitch, at the same time maintaining back pressure on the cyclic to keep the nose coming up. By the time you have turned 90º or so, your application of cyclic will have tilted the main rotor far enough back that the thrust vector is pointed ahead of the helicopter's vertical axis. From that point, increasing collective pitch and power dramatically slows the helicopter and tightens the turn; more power makes you go slower, not faster. Shortly thereafter, your landing or hover point will appear off the nose, although you may not be able to see it at first because of poor downward cockpit visibility and will have to rely on a crew member to talk you in. You align yourself on short final, reducing collective as you roll out of the turn, then increasing it as the airspeed approaches zero. By now you're about thirty to fifty yards out, and the rest is just like any other approach. To put things in perspective, you could overfly your spot at 120 knots, do a 360º turn, be in a hover above it within about fifteen seconds, and do it all within a radius of two hundred yards.
The H-53 had one peculiarity in tactical approaches; maintaining a tight level turn to the right required a nose-down attitude of 5º or so. That doesn't sound like much, and it isn't. But it looks like a lot more at 60º or 70º of bank with the treetops whistling by just outside the cockpit. It took some getting used to. Tactical approaches were demanding to fly, but with practice they became more or less automatic and encompassed everything from a full-dress approach as described above to a quick, gentle, 180º buttonhook to a touchdown. With a delicate touch on the cyclic and smooth, aggressive applications of collective to slow you down, tactical approaches could be a thing of beauty and happened with deceptive speed, seemingly in slow motion.
The H-53 was enormously capable, but there was a darker side to the story, for the Air Force versions had a hidden lethal flaw. The U.S. Navy, the Marine Corps, the Luftwaffe, and the Israeli Heyl Ha'Avir lost H-53's to enemy action, to pilot error, to maintenance oversight, and to sheer boneheadedness. They didn't lose all that many, but they did lose some. And there were survivors. Air Force H-53's went out of control, terminally and without warning, or they just didn't return. There were no survivors. More precisely, there were exactly two survivors; a pair of young pararescuemen who were sitting on the open ramp of an HH-53 with their parachutes on when it went out of control over the Tonle Sap in Cambodia in June 1973.19 The last thing they heard on intercom was a final "Oh my God!" from the aircraft commander as the cyclic slammed back into his hand. When his body was recovered, the right thumb was torn from the socket.20 By 15 May 1975, a total of four Air Force H-53's had been lost under similar circumstances, two Knives and two Jolly Greens. The total Air Force H-53 fleet numbered forty-three or forty-four at the time of the Mayaguez affair, so the loss rate for unknown causes was approaching 10 percent (the Tonle Sap crash went on the books as a combat loss to keep Rescue's safety record clean, but nobody who was familiar with the circumstances believed it).
In the spring of 1975, most thinking H-53 people considered the flight control system the prime culprit in the cause-unknown fatal accidents. What little we knew pointed to the primary flight control servos, the three large, hydraulic actuators that transferred flight control inputs to the main rotor head. The most direct evidence was from the January 1975 crash. It had occurred in daylight not far from Nakhon Phanom, witnessed by a Thai schoolteacher who had watched the helicopter go out of control and explode in flight. His description of the helicopter's final moments suggested an extreme coupled control input, that is, one that combined pitch, roll, and collective components.21 That eliminated the AFCS hydraulic servos as a cause, and the AFCS electrical system was incapable of producing forces that the pilot could not override. More conclusively, the Warner-Robins representative on the accident investigation board found a primary flight control servo retaining bolt in the wreckage that was scorched where the retaining nut should have been. That indicated that the nut, and presumably the primary servo, had parted company with the bolt before the aircraft exploded.
It was a good start, and with full benefit of hindsight that was exactly what had happened. But having made a sound deduction, Warner-Robins dropped the ball; the corrective action was to place a self-locking feature on the nut, assuming that vibration had caused it to rotate and back off the bolt. In fact, the nut had almost certainly shattered as a result of hydrogen embrittlement. Adding a self-locking feature did no good because the self-locking nuts were made by the same manufacturer using the same flawed process. The problem eluded accurate diagnosis for three more years, and at least one more H-53 was lost with no survivors.
The culprit was Warner-Robins's fixation on air refueling. Believing that aerial refueling put additional stress on the rotor head and associated components, early in the program Warner-Robins had directed the installation of extra-tough nuts to secure the primary flight control servos. This led to the procurement of the nuts, which turned out to be hydrogen-embrittled.22 Just how many of the unexplained fatal crashes were attributable to the defective nuts is uncertain, but ironically the 13 May crash was not. The accident board traced its cause firmly to a defective sleeve-and-spindle assembly, the mechanism that holds the main rotor blade to the hub and permits it to rotate in pitch. The assembly had been improperly refurbished by the Naval Rework Facility, NAS North Island, and failed in flight, allowing the main rotor blade to depart the rotor hub.23 The ensuing vibration quickly destroyed the aircraft.
The training of the Knife and Jolly Green crews that flew in the Mayaguez-Koh Tang operation differed only in detail. The 40th placed considerable emphasis on training in aerial refueling, and a number of 40th helicopters were equipped with the LNRS (limited night recovery system). This system, when everything was working, which it rarely did, permitted blacked-out approaches to a hover by means of a Doppler radar hover coupler and LLLTV (low-light-level television) setup. Select crews were required to maintain LNRS currency, although as it happened, it was of no value in either Frequent Wind or the Koh Tang affair. It is also worth noting that the LNRS system was notoriously unreliable and drove maintenance up the wall.
Pilots in both squadrons received their initial H-53 qualification training at the Air Force Helicopter School, run by the 1550th Advanced Tactical Training Wing at Hill AFB, Ogden, Utah. Currency training for both units was event-oriented; it was based on the accomplishment of specific tasks. So many precision and nonprecision instrument approaches, so many simulated day and night hoist pickups, normal approaches, steep approaches, shallow approaches, and other maneuvers were required per quarter and semiannual period. As with all Air Force flying units, the aircrew training cycle revolved around annual proficiency checks and pilots' yearly instrument checks. Traditionally, the proficiency and instrument checks were scheduled according to the individual's birthdate and were administered six months apart. But Rescue Service threw the 40th a curve by following MAC's lead and adopting the "hard crew" concept in imitation of SAC. This concept meant assigning crew members permanently to a crew that always flew together with only limited substitutions. Each crew was assigned an artificial reference date for proficiency and instrument checks and took its check rides as a unit.
The hard crew concept worked for SAC in the 1950s and early '60s. Almost all SAC flying at the time was in training flights, deployments, and check rides. Everything could be scheduled well in advance, and crews stayed together for years But it didn't work worth a flip for Rescue Service in Southeast Asia in the mid-1970's. As a result of the constant turnover created by one-year tours, the system started breaking down as soon as it was implemented. Personnel turbulence required frequent crew changes, and the reference date changed every time; that alone created a mountain of useless paperwork. To make matters worse, giving every member of a crew a full proficiency check on a single flight required some six or seven hours, and the stakes were high. The check rides tested endurance as much as proficiency. A bust by one crew member failed the entire crew, which then had to go through an exhaustive requalification program before it could fly operational missions or pull alert.
The headquarters-imposed rescue slogan current at the time was "Total Compliance!" We tried hard to comply but how closely the paperwork correlated with reality was anybody's guess. In a perverse way the slogan was totally appropriate—for a fraternal order of sadomasochists. If our currency and standardization program wasn't masochistic, I don't know what the term means.
In both squadrons, the accomplishment of required training events was closely monitored, by and large conscientiously so. The fundamental problem was that training requirements were driven by the demands of check flight criteria and revolved around stereotyped noncombat maneuvers. Given the preemptive Air Force emphasis on flight safety—or rather avoidance of training accidents—that which was not explicitly required was effectively prohibited. Tactical approaches were the primary victim. The normal, steep and shallow approaches that were part of every check ride began in straight and level flight at five hundred feet AGL (above ground level) and proceeded to the hover or touchdown point on a constant heading. Outside of a demonstration or two at Hill, they were the only kind of approach most of the young pilots had ever seen.
Although the training and evaluation system kept basic flight skills honed to a fine edge in such essential areas as systems knowledge, instrument flying, hoist operations, and aerial refueling, it let us down in gunnery, formation procedures, and tactics in general. How we trained and how we intended to fight diverged sharply, even on paper, in a classic display of institutional schizophrenia, Rescue Service regulations prohibited formation flying except in combat. The wonder is that we retained as much flexibility as we did.
The above account may make flying the H-53 for Uncle Sam's Air Force in the spring of 1975 sound like grim business, and in a way it was. A comment by a fellow Jolly Green pilot made shortly after the Koh Tang operation makes the point: "We ought to get air medals just for taking that sonofabitch off the ground." The implied reference was to the unexplained fatal accidents. Emotionally, I agreed with him. The H-53 was inherently dangerous in a way other Air Force vehicles were not, but it had its good side, too. The men who flew it in the spring of 1975 responded with a rare combination of dedication, good humor, and fatalism. I picked up a saying somewhere along the way that neatly summed it up. Flying the H-53 was like a passionate love affair with a beautiful nymphomaniac with a nasty temper and a black belt in karate: there were times when it was lots of fun, and there were times when it scared the hell out of you, but it always had your full attention.
Click Here to see what an H-53 looks like
This article excepted from A Very Short War: The Mayaguez and the Battle of Koh Tang
Number Forty-six: Texas A&M University
Military History Series
ISBN 0-89096-665-6 cloth $39.50s
LC 95-17325. 6x9. 264 pp. 21 b&w photos.
5 line drawings. 11 maps. 1 table. Apps. Gloss. Bib. Index.
Military History. Vietnam.
Publication Date: November 1995.
FOOTNOTES
[1]William R. Fails, Marines and Helicopters, 1962-1973, pp. 12-13, 60. H was for helicopter, R for cargo, and S for Sikorsky; 2 indicated that it was the second Sikorsky-built navy cargo helicopter. The army designation was H-37.
[3]Fails, Marines and Helicopters, p. 13
[4]Ibid., p. 60.
[5]Ibid., pp. 58-59, 62.
[6]The CH-53E, the standard marine heavy-lift helicopter has a seven bladed main rotor and a larger tail rotor with the pylon tilted to provide additional lift. The MH-53J Pave Low III emerged from the ARRS night recovery system program to give combat rescue forces a low-altitude, night, and adverse-weather capability. It is fitted with terrain-avoidance radar and FLIR (forward-looking infrared), fully integrated into the avionics system. Originally fielded as the HH-53H, all Pave Lows were transferred to special operations with the disestablishment of ARRS in 1989. All air force H-53s have since been upgraded to J-model, Pave Low III standards.
[7]Even as the air force H-53 program was getting underway, the air force relinquished to the army all combat helicopter missions except for rescue and special operations in return for army abandonment of fixed-wing ground-attack and cargo aircraft (Richard 6. Davis, The Thirty-One Initiatives [Washington, D.C.: 1987], pp. 19-22).
[8]The navy SH-3A/B was amphibious and had a boat-type hull with strut mounted pontoons for lateral stability on the water The air force CH 3C, on which the HH3E was based, had sponsons instead of pontoons and was fitted with a rear cargo ramp.
[9]Air Rescue Service issued a requirement for a helicopter aerial refueling capability in 1964. Preliminary flight tests with a dummy refueling probe on a CH-3C were conducted in December 1965, and the first in night fuel transfer from a CH-130P took place a year later (Tilford, Search and Rescue in Southeast Asia, pp. 82-83). The driving force behind this radical development, which many believed to be infeasible, was the H-3 Systems Project Office at Wright-Patterson AFB, Ohio, notably Maj. Harry P. Dunn, who pushed the concept earliest and hardest; James Eastman, and Richard Wright, who, along with Dunn, planned and flew the early flight tests.
[10]Probably the best of these was the West German M3, which fired the same 7.62-mm round as the minigun, weighed about twenty-six pounds, and had a cyclic rate of 1,200-1,300 rounds per minute. The U.S. M60 infantry machine gun, later mounted on the HH-3E, was even lighter at twenty-three pounds but fired only 550-600 rounds per minute -- in my judgment, marginally adequate. I became involved with helicopter armament issues as ARRS chief of tactics in 1978-79. The above is based in part on rescue's institutional memory of the original armament decision.
[11]Tilford, Search and Rescue in Southeast Asia, pp. 90-93.
[12]The array of technical orders for air force aircraft begins with the basic flight manual, in this case TO. 1H-53(H)B-1, or the "dash one." The -2 is the organizational maintenance manual, the -3 is the structural repair manual, the -4 is the illustrated parts breakdown, the -5 contains the basic weight checklist and loading data, the -6 is the functional check flight manual, the -9 is the cargo-loading manual, and the -21 is the aircraft inventory master guide. This only scratches the surface.
[13]Information to the author, Lt. Col. Vernon Sheffield, 9 January 1991.
[14] As a result of the advent of fixed-wing aircraft with negative static and dynamic aerodynamic stability controlled with fly-by-wire systems, this generalization is no longer strictly correct. My reference here is to classical aerodynamic theory and mid-1970s technology.
[15]Air force regulations required the use of oxygen above an altitude of ten thousand feet MSL (mean sea level); however, the requirement could be waived for brief exposure. In practical terms, eleven thousand feet was the service ceiling for the H-3 and H-.53, and we rarely stayed above ten thousand feet for long.
[16]T.O. 1H-53(H)B-1 (1 November 1973), 3-9, fig. 3-3.
[17]The dash one followed the ring vortex theory, but in muddy wording that inspired little confidence (TO. 1H-53[H]B-1 [1 November 1973], 6-1).
[18]Including, for the record, the T-37, T-33, H-19, H-21, H-3, and C-131/T-29, plus assorted light aircraft.
[19]Author's notes of ARRS/MAC H-53 briefing, 2 December 1977, Scott AFB, Illinois (henceforth ARRS/MAC Brief), a summary briefing of all air force H-53 accidents prepared and given by an ARRS/MAC standardization-evaluation team.
[20]Review of the accident report and discussion with one of the pararescuemen in question, Eglin AFB, Florida, spring, 1974.
[21]Author's journal. I read the accident investigation report as soon as it was released.
[22]ARRS/MAC Brief.
[23]Findings of the Collateral Board Investigation. I conducted the investigation.
