Escaping from test VC10s and One-Elevens
Many civil aircraft have escape hatches fitted utilising the freight door to allow departure from the aircraft.
The original forward escape hatches on the One-Eleven and the VC10 were of a similar design concept. Essentially, a door held in place with explosive bolts replaced the freight door. On firing the bolts, levers on pretensioned torsion bars attached to the inside of the fuselage lowered the leading edge of the door into the airstream, which caused it to fly away. Any residual cabin pressure assisted the operation. There was a large duct, or trunking, fastened flush with the cabin floor and to the freight door surround for the crew to jump through. Within the duct was a spring-loaded blast shield that normally projected above the floor. It dropped down to project into the airflow on jettisoning the freight door. The function of the blast shield was to allow escapers to clear the fuselage and to progressively decelerate them to the speed of the airstream, rather than for the deceleration to be instantaneous. The duct and blast shield were of sheet metal skin, stringer and rib construction. The freight bays were sealed from the cabin, to be representative of production aircraft in this respect, so that associated flight and ground testing could be conducted. The escape drill was to depressurise the cabin before firing the escape hatch.
During the incident on the prototype VC10, G-ARTA, on December 31, 1963 the behaviour of the aircraft was rather alarming so the escape hatch was fired at full cabin differential pressure, around 8 p.s.i., in case the aircraft broke up before the crew could escape. Consequently, the duct in the freight bay and the cabin floor had to instantaneously withstand this differential pressure because the freight bays were not vented. This resulted in the escape chute being crushed and much of it tore out of the aircraft. Moreover, many areas of the cabin floor buckled, including the floor beams, which contained the flying control cable runs.
Following the G-ARTA incident, it was recognised that there could well be circumstances where there would be insufficient time to depressurise the cabin before needing to escape. To overcome these problems, all test One-Elevens with escape facilities, subsequent to G-ASHG, had beefed up escape chutes; i.e. G-ASJA, G-ASJC, G-ASJD and G-ASYD. (G-ASJB was scheduled to undertake performance and crew training, therefore, did not need escape facilities due to the low risk nature of testing, though she did have a rear escape hatch.) Constructing the escape chute and the blast deflector from thick (approx. 1.5”), high density and multi-laminate plywood did this. Moreover, front and rear freight bays were adequately vented to the passenger cabin. Indeed Concorde’s facilities were similar to the modified One-Eleven system.
A lever was added outboard of the co-pilot’s seat which mechanically opened the pressurisation control valve to rapidly depressurise the cabin so the door in the rear pressure bulkhead could be opened to give access to the escape hatch in the rear ventral door.