The final installment of a three-part history of modern Western aircraft ejection seat systems. (The accompanying image shows an ejection seat developmental test).
A Brief History of the Development
of Western Aircraft Egress Systems:
(Part Three of Three)
REFINING THE ORIGINAL CONCEPT: THE UNITED KINGDOM
As research and development of seat technology gained momentum in the decade following the end of the Second World War, there were at least two other companies involved in production of ejection seat systems for high performance aircraft, in addition to the well established Martin-Baker Aircraft Company. These were the ML Aviation Company and the Folland Aircraft Company, Ltd.
ML Aviation, under the direction of Belgian engineer Marcel Lobelle, produced a series of seats from the ML Mk.I through the ML Mk.IV. The first two seats were fitted into production aircraft in use by the RAF and were manual (not automatic) systems very much like the M-B Mk.I. The Mk.III and Mk.IV were automatic seat designs (fully automated sequencing, with man-seat separation and deployment of personal parachute), but according to B. Philpott were not installed in active service airplanes. The earlier two seats were used experimentally in several aircraft types (including Meteor and Wyvern types) but in 1951 an experimental Hawker fitted with an ML seat crashed, and there was speculation that the pilotís seat had somehow failed. Shortly thereafter the company ceased production of egress systems and focused on other aircraft sub-component manufacturing.
The Folland Aircraft Company of the UK acquired licensing rights to produce the Swedish SAAB Type 29 seat (as fitted to the SAAB J29 aircraft), but modified the system to provide for automatic release before incorporating it into their Folland Gnat, a lightweight, sweptwing fighter/trainer used by India, Finland and a few other nations with some success. Folland was not interested in continuing the production of egress systems, beyond that of the Gnat, and it wasnít long before the only UK egress system manufacturer was the Martin-Baker Aircraft Company.
The Folland Gnat egress seat was a lightweight, simplified system, which suited the perceived need at that time for use of lighter ejection systems for aircraft which were becoming increasingly more complex and much heavier. Englandís Martin-Baker also felt the need to reduce the weight and bulk of its seat design (the Mk.III) in keeping with this philosophy, and consequently this led to the development of the M-B Mk.IV seat. Naturally, it was important to achieve this weight reduction without significantly altering the level of egress effectiveness which the Martin-Baker systems provided. This was achieved by incorporating a redesign of several key components in the guide-rail/track system and seat framework support structure. The seat pan and parachute pan units were retained with slight modifications, as were the twin-drogue system and the 80 ft/sec ejection gun. The Mk.IV seat incorporated for the first time a between the legs ejection handle as a secondary means of actuation ejection, since it had been determined that in certain situations the effects of adverse inertia and G loading made it difficult to use the conventional face-curtain actuator. (This began subsequent engineering conjecture over the question of whether or not to focus on use of one actuator only, for a number of years, which seems to have ultimately led to final selection of the between-the-legs actuator design as found in the most recent M-B systems).
The parachute and sea-survival/inflatable raft kits were redesigned for use on the new Mk.IV seat, and this was prompted in part by the need to improve pilot comfort as well as fit the overall seat modification requirements. Further improvements consisted of an integrated seat and parachute harness system, eliminating two separate harness systems; the system was controlled by the M-B Timed Release Unit (TRU) and was so effective that it was retrofitted in some cases to older Mk.III seats. The new inverted U-shaped personal chute assembly was placed higher up in the seat back, just under the drogue/head-box container, which positioned it more efficiently for simplified deployment. Sea-survival/inflatable raft (usually made to order by Martin-Baker for the specific requirement of the contracting nation) was stowed in the seat pan, under the pilot, and a specially designed, high-density, slow-acting foam rubber material was used in the seat cushion over the kit to reduce the possibility of spinal injury due to effects of acceleration overshoot. One final refinement was the addition of a G sensing switching unit in the TRU which permitted either standard drogue deployment delay of 1Ĺ seconds (at low speed, low altitude), or delayed drogue deployment appropriate to the negative G force loading imposed by deceleration. The M-B 'guillotine' device for cutting the drogue withdrawal line to the seat was also used for the first time in the Mk.IV seat, a feature which has remained an important component of M-B automatic seat systems. Modification was also made to the leg restraint strap system. The idea of incorporating built-in rigid foot rests had been long since discarded on M-B seats (most American seats built in the early 1950s also used the rigid footrest feature, although this was also discarded by US seat manufacturers in the mid 1950s, in favor of the leg restraint strap concept).
The next step in M-B seat development, the production of the Mk.V seat, was substantially influenced by the M-B/US Navy ties referenced in the previous chapter. Largely due to the requirements of the Navy, the basic Mk.IV seat was structurally modified to withstand greater deceleration loads (40 negative G, instead of 25), as was the seat harness system. Featuring the 80 foot per second ejection catapult and most of the features of the Mk.IV seat, the new US Navy specification Mk.V family seat began service in the late 50s and early 60s, and was eventually installed in over 20 different American aircraft types (this includes the later Mk.VII rocket powered version, which was markedly similar to the Mk.V but featured the installation of a rocket unit under the seat-pan). Most of the US Navy Mark.V seats were upgraded to the later, rocket-powered Mk.VII version at a later date. The Mk.VII seat featured a prominent change in the personal parachute container component, which was manufactured in an inverted U-shape of fiberglass (in contrast to the shaped metal parachute fitment shroud and U-shaped fabric parachute pack in use on the Mk.V), and had two compressed springs situated between the seat structure and the container to help fling the container somewhat out and clear of the seat on chute deployment (it remained tethered to the seat, however). There were also minor changes in the thigh portion of the seat pan. Suffice it to say that the addition of a rocket power unit to the Mk.IV and Mk.V seats resulted in the Mk.VI and Mk.VII seats, although that is considerably oversimplifying the process.
In the early 60s, many American aircraft purchased by NATO nations began to be fitted with Martin-Baker Mk.V seats. Norway was the first nation to have the American manufactured ejection seats in its F-86 and F-84 type aircraft replaced by Mk.V units, and Germany and others shortly followed suit; Denmark had much earlier (in 1950) placed an order for a number of UK Meteor fighters fitted with the Mk.I seats, demonstrating the design effectively to the rest of Europeís allies.
Several other specially designed seats produced by Martin-Baker were their rear-facing ejection seat design (first live-fired in 1960, proving the concept) for UK 'V-bombers,' and a Mark.V based egress system configured to fire underwater, eject the pilot from his ditched aircraft, inflate his life-vest and bring him to the surface automatically, even if he is unconscious.
As mentioned earlier, the purpose of the rocket-seat development program at Martin-Baker was principally to provide enhanced low-level escape. The original Martin-Baker rocket unit was a twin-tube design with an adjoining nozzle chamber, fitted under the seat and firing downwards. This system was first successfully tested with a 'live ejection' in April of 1961. M-B rocket seat systems strive to ensure a near vertical trajectory away from the disabled aircraft. This is allowed owing to the fact that the M-B seat uses a conventional ejection gun and separate rocket propulsion system which are sequentially actuated by the egress systemís automation. This stands in marked contrast to other systems, such as that routinely employed by most US manufactured ejection seats of the 1960s, which combined the ejection catapult and rocket charge in a single gun. The combined gun system functions as a standard explosive charge ejection catapult until the automatic sequencing device allows it to discharge the rocket charge rearwards at a 45 degree downward angle, thereby achieving a slightly less vertical, 45 degree upwards and forwards trajectory.
The combined gun concept is less desirable for low level and 'unfavorable aircraft attitude' situations (nose down, low level, low speed), while the separate rocket pack approach allows, in theory, more altitude to be gained in a vertical plane for safe chute deployment and recovery. Martin-Baker was a pioneer in developing this system at a time (1960s) when most other seat manufacturers retained and used the less ideal, although somewhat simpler, combined gun system.
Mentioned earlier, one important modification of the UK's Mk. VII series was specifically designed and fitted to the Lockheed F104G Starfighter (export version for NATO, particularly used by West Germany in extensive numbers). This seat was the M-B Mk. DQ-7 seat. After a series of severe pilot injuries were experienced by aircrew upon emergency ejection using this seat, an investigation showed the cause to be due to the pilot's knees fouling on the forward instrument panel of the Starfighter cockpit. Resulting modification of the seat's main chute containment system, which allowed placing the pilot further aft in the seat, resolved the difficulty. This and subsequent seat modifications led to adoption of the M-B Mk. GQ-7F in Starfighters, with the final modification designated the Mk. GQ-7W. This seat is still in service with the Italian Air Force's Starfighters, as Italy acquired the remainder of former German F104Gs when that nation replaced its Starfighters with newer aircraft.
Another very important seat used extensively by the USN in The F14 Tomcat, and also a derivative of the Mk. VII series seats, was the M-B Mk GRU-7A seat. This seat featured enhanced features, updated system components, and weighed slightly less than the earlier Mk H7AF type seat. This seat has seen extensive service with the US Navy's Tomcat squadrons and has an exemplary survival rate in emergency egress situations--many of which have taken place on or just off of carrier decks.
From the US inspired Mk.VII seat, the next step up for Martin-Baker was development of the Mk.VIII seat; this unit was specifically produced to meet the requirements of the high-performance, experimental TSR-2 aircraft. Although the TSR-2 never flew, the developmental work accomplished by Martin-Baker on the seat formed the basis for a whole new generation of ejection seats that would shortly result in the Mk.IX, Mk.X series, and the latest, high technology Mk.XIV seat.
The entirely redesigned Mk.VIII seat was the first major departure taken from the previous generation of M-B seats and set the style for the current Mk.X and Mk.XIV seats. Among the refinements of the Mk.VIII seat was the elimination of the face-blind ejection actuation feature, a between the legs grab-handle being used exclusively.
Also featured was a multi-tube rocket powered unit with twin chamber nozzles and use of the head-rest/drogue containment area for placement of the personal parachute. A special power retraction system was installed which acted to pull the pilot into a favorable ejection position, very much as an earlier unit mounted on the US Navy Mk.VII seats did. Additionally, a remotely actuated rocket firing system was fitted which was a considerable improvement over the previously used rocket actuation device.
The new Mk.IX seat of the mid-to-late 70s benefited from the Mk.VIII development, and with this unit Martin-Baker seats underwent a major reconfiguring.
One result, aside from significantly enhanced function, was considerable aesthetic improvement in appearance. Most components of the Mk.IX seat were reworked and advanced features found on the experimental TSR-2 seat were incorporated in the new Mk.IX series seats. These included an entirely new gas actuated seat firing system replacing the previous cable linkages. The face-blind actuator system was discarded in favor a between-the-knees grab handle since studies indicated that such a system was faster to use than a face-blind design (additionally, modern crash helmets provide considerably improved wind-blast protection, making that former function largely redundant). The power retraction system was further improved, and the personal parachute containment area was placed lower in the seat-back, behind a contoured back-rest.
Additionally, the seat and back pan assembly was fitted so that it could be quickly removed from the central seat structural members for ease of cockpit maintenance. The Mark IX series seats were installed in Harrier and Jaguar aircraft, for the most part, and their design trends were reflected in the development of the even more improved Mk.X series seats which followed.
Perhaps the most significant improvement found in the M-B Mk.X seat is the incorporation of the pilotís personal parachute into the head-rest structure containing the drogue system. This is a concept which now appears to be adopted almost universally by egress seat manufacturers; it is now used successfully by the American Stencil Aero Engineering Corporation in their AV-8A (US spec Harrier) Stencil SIIIS seat, as well as by McDonnell-Douglas in the ACESII system. The head-rest container appears to be advantageously sited for optimal deployment of the main (pilotís) recovery chute and permits simplified, efficient automatic deployment operation. Other improvements found on the Mk.X seats are an extended gas-actuation system, a simplified two-point aircrew harness system, an arm restraint system (in use on the SAAB Gripen and the UKís Tornado aircraft), and complete design of the drogue gun and barostatic time-release mechanism. The pilotís personal chute uses a GQ Aeroconical canopy design which permits rapid deployment with reduced susceptibility to severe deceleration forces, and the combined drogue and main chute placement concept allows greater ease in servicing by ground personnel in that the entire combined chute system is removable as a unit. The Mk.X series seats are specified to permit zero/zero operation and safe ejection at speeds up to 630 knots IAS.
Mk.X type seats are used in a variety of aircraft, including the MiG-19 (Pakistan), the Hawk, Tornado, Macchi MB339, CSA 101, Sea Harrier, Northrop F5, SAAB JAS 39, Nanchang A5, K8/L8, the Lavi, and a number of other types in use around the world. Variations belonging to the Mk.X family are the Mk.X-L Lightweight ejection seat and the Mk.X-LF (Northrop F5 upgrade seat); all feature similar systems and specifications / performance capabilities.
The Mk.X-LF is a special retrofit for the Northrop F5 Freedom Fighter which is in use my many nations using that aircraft. The original Northrop seat proved ineffective for low level safe pilot recovery, and therefore selection was made of the Mk.X-L lightweight version of the Mk.X for use in it. (By example, the original Northrop seat provided safe recovery at 1720 feet AGL, at an IAS of 400 knots and a dive angle of 45 degrees. The figure for the M-B seat in identical speed and dive is only 625 feet AGL).
Another more recent Martin-Baker seat is the Mk.XI seat, based upon the successful lightweight seat used on the T-27 Tucano turboprop trainer. The Mk.XI is designed for use in medium performance propeller-driven aircraft and does away with the rocket pack while still providing ground level/60-400 KIAS performance. It features all the advancements of the Mk.XIII (TSR-2) seat, but with substantially less weight.
The Martin-Baker Mk.XII seat is a development of the Mk.X, and very similar to it, but employs pitot-type air and motion sensors to actuate the appropriate safe egress sequencing. Two extendible pitot sensors (one mechanical and the other electrical) on the side of upper seat structure are part of a three component system which determines a variety of parameters to facilitate egress actuation in any of three modes: low level/low speed, low level/high speed, and high level (speed is not factored in in this mode).
Furthermore, the seat sensors permit control of parachute deployment in such a manner as to minimise damage which may occur due to severe high-speed ejection forces. The Mk.XII also features a much reduced maintenance requirements which permits a one minute daily inspection for functional readiness, and a three-year servicing schedule.
In 1985 M-B received a contract to produce the Mk.XIV seat for use in the US Navyís F-14 Tomcat, F/A-18 Hornet, and T-45 Hawk aircraft. This was designated the high-technology NACES, or Naval Aircrew Common Ejection Seat. Utilising the latest in microprocessing technology, the Mk.XIV seat features enhanced operational sensors which permit much greater levels of safe operation in a wide variety of speeds, combat attitudes and altitudes.
Yet another M-B seat is the Mk.XV seat, which was originally developed for use in the Pilatus PC-7 aircraft. An ultralight seat design with a rocket power pack, the very compact Mk.XV seat permits ground-level and 60 KIAS, to 350 KIAS operation in medium performance propeller-driven aircraft. Through canopy ejection is provided as a contingency. Total weight of the seat is only 80 pounds.
The latest and most advanced Martin-Baker ejection seat available at this writing is the lightweight, high-technology Mk.XVI seat. This seat, designed specifically for the latest generation, high-performance lightweight aircraft such as the European Eurofighter and Rafael, features advanced 2nd generation state-of-the-art electronic & microprocessor controlled systems to assure the highest optimal survival margin for aircrew operating the most recently developed aircraft. Offering zero/zero operation and up to 600 KIAS and 50,000 feet operation, the Mk.XVI seat features a weight/mass reduction of 30% over previous seats by combining the twin-catapult gun tubes with the seat structure itself as structural members. Developed as a variant, the Mk.US-XVI-L seat is a special model designed to meet the US JPAT (Joint Primary Aircraft Trainer System) requirement for a lightweight, advanced egress system. Featuring similar specifications to the Mk.XVI, the variant weighs only 125 pounds with full kit and components, and performs safely from zero/zero to 450 KIAS and 40,000 feet altitude. Important also is the seatís reduced maintenance requirement, which improves on previous late-generation M-B seat standards.
MODERN AMERICAN ADVANCEMENTS: ACES and ACES II
The development of American Air Force ejection seat research continued in the late 60s period with refinements of the Douglas Escapac IC system that led to a new phase of work, conducted under the aegis of the Douglas Aircraft Division of the McDonnell-Douglas Corporation, and based on enhancements to the proven & successful Douglas Escapac system. With Air force use of aircraft originally developed for use by the US Navy (F-4 Phantom II and the A-7, most notably), the merits of the excellent Escapac family of seats became clear and McDonnell-Douglas was charged with principal responsibility for a new, substantially improved system Air Force egress system termed the ACES, or Advanced Concept Ejection Seat.
While work continued on the McDonnell-Douglas ACES program, Stencil Aero Engineering Corporation (Formerly a division of Talley Industries that is now owned by Universal Propulsion Co., Inc.), which had been actively designing and testing aircraft escape systems for military use at both China Lake NOTS and its privately owned Utah rocket sled facility at Hurricane Mesa for years, fielded the other major American seat system recognized as being in the forefront of US seat technology. Stencil innovations included the DART seat stabilisation package that was retrofitted to most older USAF ejection seats, a line of highly engineered and reliable seat initiation and actuation components, and several well conceived and innovative ejection seats that were noted for their structural integrity, light weight, and reliability.
The Stencil SIIIS-3 series of seats was designed to meet the US Navy's requirement for the American AV-8A Harrier and ended up being used in the German Luftwaffe's Alpha Jet aircraft. It was also used at some time in the early F-117 Stealth production aircraft, the Navy F-18 prototype, and the early F-16 FSD aircraft. The Stencil seats departed from prior American designs in incorporating a fiberglass seat pan that covered a soft nylon seat survival package (much like the early USAD MD-1 survival seat kit concept), replacing the entirely "hard" seat kit that was used extensively in the Century Series era aircraft (this return to a previously explored concept was also a feature of the McDonnell-Douglas ACES technology). Stencil was acutely aware of the tendency of ejection seats, both American and foreign, to become excessively ponderous and heavily constructed and favored early development of so-called 'lightweight' designs (such as the NAA LW series seats). Stencil seats incorporated a rotating seat kit feature that aided in man-seat separation and used leg restraints and used a series of fail-safed ballistic chute deployment devices. Original SIIIS-3 seats featured a US Navy type face-blind actuation system as well as a between the thigh grab handle actuator, but this was later deleted in favor of the grab handle system. A version of the seat also was produced using standard USAF arm rest grip actuators, which was flown in the early F-117 stealth aircraft.
Another Stencil innovation was the RANGER rocket extraction system that was similar in concept to the Stanley YANKEE system (used in the A-1D 'Spad') and employed a rocket boosted device that pulled a crew member from a stricken aircraft (this concept was further explored in the aftermath of the NASA Challenger disaster, as a possible egress system usable on the space shuttle).
Other seats designed and produced by Stencil included the SIIIS-3RW 'reduced weight' seat, featuring all of the original SIIIS-3 performance, but with a 20% further reduction in overall weight, and the S4S system for use in advanced, high performance jet aircraft. Stencil seats have been used in the US AV-8A & AV-8B Harrier aircraft, several nation's ALPHA jets, the Argentine AF's IA-63, the Japanese Self Defense Air Force's T-4 trainer, and several other types of aircraft, both jet and propeller driven. Although somewhat eclipsed by the USAF's choice of the McDonnell-Douglas ACES system, the Stencil seats remain examples of the finest American egress technology in recent decades.
Meanwhile, the US Air Force adopted the Escapac system, but made basic improvements to the US Navy system to enhance low-level, low speed performance characteristics. This included replacing the Navy's RAPEC I rocket catapult with a higher rated rocket impulse unit (RPI-2174-16) and adding a zero-delay parachute lanyard to increase escape capabilities. The higher energy rocket increased trajectory height and the zero-delay lanyard improved early chute deployment performance to give true zero-zero operation. The high speed capabilities of the Escapac IC system remained unchanged, allowing excellent survival margins at the upper reaches of the operational envelope. Thus modified, the IC-2 seat (used in the USAF A-7D), permitted escape from ground level and zero knots through 600 (or more) knots at altitude. However, despite additional refinements that led to development of the IC-7 seat (used in the early F15A and F-16), it was clear that much work remained to ensure the greatest level of safety for emergency escape by aircrewmen from all corners of the envelope--not just in the specific zero-zero and high performance modes.
A study of emergency Air Force crew ejections over the previous years indicated certain inadequacies of design concepts that were established standards in existing systems. Chief among these problem areas were recovery parachute deployment timing, rocket-burn stability problems, and man-seat separation issues.
The ACES attempted to address all of these areas of concern and it was well noted by US designers that attempts had already been made to correct similar problems in several European seat systems by that date (1970). In an effort to improve system ejection timing sequences, the ACES adopted a refined three stage approach that attempted to reduce the inherent tolerances in the timing sequences through use of more sophisticated electro-explosive actuators (previous actuator components had been largely explosively driven and mechanically timed). Low level/low speed considerations were given higher priorities than had been previously accorded. The matter of rocket burn stability, which had previously been adjusted via aerodynamic devices such as projecting booms, vanes, and parachutes, was corrected to a great degree through use of a gyro-controlled vernier rocket unit (STAPAC). Man seat separation concerns, which in past American seats had been addressed through such devices as rotary actuated straps (Weber and others), inflatable bladders (Escapac), and snubber systems (Stencil DART system--Directional Automatic Realignment of Trajectory), were broached through adoption of a European system in which the deployment of the main recovery chute pulled the occupant from the seat. It was determined that this last approach satisfied concerns over man-seat collisions, additionally. Automatic ejection responses conformed to one of the following three general conditions, to assure the best response consistent with physiological limitations: 1) Low-speed mode (below 275 KEAS, Below 15,000 ft altitude); 2) High-speed mode (Above 275 KEAS, Below 15,000 ft altitude); 3) High-altitude mode (above 15,000 ft altitude).
The ACES seat's physical structure followed lines established by the NAA LW-3B design and the M-B Mk. 15 concept, which optimised lightweight design characteristics, and upper structures were somewhat lessened so as to increase rearward/lateral visibility. The ACES seat fired through actuation of conventional hand-grip control handles, located at the forward bilateral edges of the lower front seat pan (much in the manner of the Weber seats). Catapult values of 18 Gs and 250 gps rate of onset were established as a practical upper limit across the whole range of temperatures and ejected weights. High sink-rate and unfavorable attitude situations were factored into the staging of the catapult main thrust rocket. A pitch control subsystem, linked to the STAPAC components, was configured that offset to a great degree previous thrust centerline sensitivities peculiar to rocket powered systems. Finally, a mortar deployed main recovery chute system was adopted that would most adequately address all points along the anticipated deployment curve (zero/zero to high speed/high altitude); this ejected the 28 foot flat circular main canopy, the inflation of which was also adjusted to ejection parameters by a controlled reefing system.
Additional refinements involved a new configuration for survival kit construction, as the previous all-rigid seat kit design had certain inertial characteristics that were less than desirable in many weapons delivery and ACM profiles. In the ACES system the walls and bottom of the seat's bucket provided the rigid containment needed for the kit contents, allowing a soft (non-rigid) kit configuration to be employed. The non-rigid kit contained two subsection containers, one of which contained items needed quickly (termed the 'hit & run' kit) that could be scooped up and carried quickly off to a position of cover. Emergency oxygen capability came from a seat mounted bottle/regulator assembly.
Additional work with the ACES system led to a further improved McDonnell-Douglas ACES II rocket propelled ejection seat system, which has since been installed on most modern American combat aircraft. The Advanced Concept Escape System II (ACES II) followed the years of research and investigation spanning the 1968 through 1975 period that produced the original ACES system just referred to. Chief advances on the ACES II Seat are a gyro-stabilised vernier pitch-control rocket, a sustainer rocket, and a controlled force catapult, which together ensure a much greater range of safe ejection attitudes and situations. The system actively monitors (or senses) environmental conditions such as airspeed, temperature, and altitude, and uses a microprocessor controlled electro-explosive system to properly sequence ejection events so as to safely slow, stabilise and recover the crewman from any point within its performance envelope (which is from zero/zero to over 600 knots IAS). The system is claimed to be so effective that it permits escape from an inverted position 155 feet off the ground and from ground level up to 50,000 feet altitude. As might be imagined, much of the earlier Douglas Escapac RAPEC work helped in laying the groundwork for the ACES I and II systems.
The ACES II system utilises an upper seat mounted main parachute configuration, similar to but significantly different from the latest Martin-Baker seats, and is specifically designed to minimise adverse ejection forces such as tumbling and excessive parachute opening shocks. An under-seat non-rigid survival kit is employed in the conventional manner, similarly as was the ACES I counterpart. In 1977 McDonnell-Douglas was awarded a contract to produce the ACES II High Technology Ejection Seat for use in A-10 Thunderbolt, F-15 Eagle and F-16 Fighting Falcon aircraft, following what the company terms a 'fly before buy' competition. This culminates the production of more than 6800 ejection seats by the company, according to their statistics. The ACES II system was also installed in the Lockheed F-117 stealth fighter, as well as the Rockwell B-1B and Northrop B-2 stealth bomber. Each application has a slightly customised configuration (for instance, the F16 seat is actuated with a between the legs D-ring, while the B-1B seat has the original bilateral front seat pan control grip actuators first employed by the ACES I seat.
While the ACES II system was until recently arguably the best system American had to provide aircrew escape (the Stencil systems providing much the same capability), the latest American egress technology program is currently underway at this time, being conducted by Boeing in cooperation with the US Air Force. Designated the CREST program (CRew EScape Technology), the purpose of the research is to produce a new generation egress system for the next wave of advanced combat aircraft. Performance criteria for the new open-seat system are reputed to be zero/zero to 70,000 feet and up to Mach 3 speeds, with an 'adverse flight configuration' low of 100 feet altitude. The CREST rocket propulsion system will feature 6 to 8 propellant chambers, containing about 60 pounds of propellant, with twin-omni directional thrust nozzles under the control of a microprocessor command unit which has been programmed to recover the pilot from all possible attitudes.
Additionally, the three-part seat program will result in a seat that also provides aircrew protection against high G forces and unusual physical effects while in the aircraft. This is partly required by emerging technologies that include use of what are termed 'inherently unstable aerodynamic aircraft' (or aircraft which must be flown with the assistance of computers to maintain aerodynamic stability in flight), and thrust vectoring systems that allow for a far broader range of maneuvering capability with resultant new and unconventional G forces.
It is interesting to note that most recently, a program was also underway in the United States to study the effectiveness of Russian egress systems, the exceptional capabilities of which were most dramatically demonstrated to the whole world by an almost miraculous pilot recovery at the Paris Air Show several years ago (1989), when the Russian pilot's MiG-29 aircraft was literally impacting the ground in a semi-inverted, extremely disadvantageous attitude. Of note are the many advanced features of the Russian seats, and their exceptionally favorable recovery rates, which have been until recently all but ignored by Western egress systems researchers. Much work remains to be done on this but there was at least one cooperative study has been completed investigating the possibility of integrating Russian seats (and/or their technology) into modern high-performance American aircraft--something that would have been inconceivable prior to 1989.
At this time (3/2002) , the decision has been made to continue developing and using US egress technology in the latest US combat aircraft (F-22 Raptor and XF-35 Strike Fighter) programs.