The Ejection Site
The ACES II Seat: History
The Advanced Concept Ejection Seat (ACES) Was developed to provide a standard Ejection seat to be utilized in all United States Air Force jets from the mid-1970s. It was first flown in a A-10 Thunderbolt II from the Fairchild Republic Co. at the Farmingdale Long Island (N.Y.) plant in April 1978. The driving reasons for the development of the ACES II were to standardize on one type of ejection seat*- this would lead to reduction in training of both mechanics and pilots, also the design was intended to provide better performance in low altitude/adverse attitude conditions as well as to improve high speed seat stablity. It also allowed the government to purchase larger lots of spare parts.

The initial ACES II production contract was awarded to McDonnell-Douglas Corp. (MDC) in November 1976. The contract was a 'Leader/Follower' type contract which meant that MDC would be the Leader and would train the Follower to build the seat as well. Weber Aircraft Co. (WAC) was selected and trained as the follower. Thereafter, each additional contract from 1982-1990 was bid upon by both MCD and WAC, with the competition helping keep the unit cost low. In 1990, with fewer seats to be ordered, the entire production was awarded to McDonnell-Douglas Corp.   Soon thereafter Weber Aircraft Co. ceased manufacturing ejection seats and concentrated on the manufacture of crew seats.

Production of the seats has totaled about 8000 as of May 1997, with some 416 non-combat and 10 combat ejections worldwide. The official USAF success rate is 94.4% in envelope, and 89.9% including out of envelope ejections. MCD manufactured some 6500 and WAC the remaining 1500.

Since its development it has been used in various forms in the following aircraft:

F-15 EagleHas add-on Canopy Breakers
F-16 Fighting Falcon Center pull W/Trajectory Divergence rockets
A-10 Warthog
B-1B Lancer With arm and leg restraints
T-46AWith Asymetrical Canopy Breakers
B-2 SpiritHas Flip-up Pitots
F-22 Raptor See The YF-22 Raptor page

The ACES II is a third-generation seat, capable of ejecting a pilot from zero-zero conditions up to maximum altitude and airspeeds in the 600 KEAS range. The peak catapult accelleration is about 12g, with a extra 2g pulse from a stabilizing rocket. The ACES II has three main operating modes, one each for the low speed/low altitude, medium speed, and high speed/high altitude. In Mode 1, which includes 0-0, the parachute is inflating in less than two seconds. In Mode 2 the chute is inflating in less than 6 seconds. Mode 3 deployment is delayed by the sequencer until the seat-man package reaches either Mode 2, or Mode 1 conditions, whichever comes first.

Note: Prior to the ACES II becoming standard, most aircraft manufacturers manufactured their own seats, or had one manufactured to their specifications. This lead to a wide variety of seats in use, with a wide range of operating envelopes. It also meant that the mechanics working on the seats had to be familar with the individual seats mechanisms and specifications. Spare parts would have to be purchased in lot sizes determined by the number of aircraft in the inventory. With a standard seat, the lot sizes for many of the parts would be larger, allowing for some savings in purchase price.

Technical Information on the ACES II seats is available here

The Ejection Site Home
Send email to Kevin