The Ejection Site - Discussion of Airliner Ejection Seats

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A discussion on the feasibility of equipping commercial airliners with ejection seats.
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  The Ejection Site Discussion of AirlinerEjection Seats  The Ejection Site - Discussion of Airliner Ejection Seats.docx The Ejection SiteDiscussion of Airliner Ejection Seats Airliner crashes cause the deaths of hundreds of people in a single incident causing them to beone of the most publicized forms of death. Often in the wake of a disaster such as the TWA Flight800 crash people ask my opinion as to why Airliners are not equipped with ejection seats. Thefollowing is my personal analysis. Concept: Passenger Survival Systems for Commercial Aircraft:especially considering Ejection SeatsDescription of system: All passenger seats to be replaced with a seat capable of being jettisonedfrom aircraft ON PILOT or COCKPIT CREW COMMAND. The seats are to be outfitted with arecovery system (parachute ) to lower the seat occupant to the ground safely. The Crew seatswould be similarly equipped. Pro: Safe recovery of passengers in the event of a catastrophic disaster. Con:  1.   Danger to maintenance crews2.   Danger to passengers due to accidental discharge3.   Possible injuries to passengers due to use4.   Weight increase5.   Larger seat area requires fewer seats in given area6.   Egress hatch requirement requires considerable redesign of cabin fuselage7.   Cost- Ejectable seat would add costs for:a.   Redesign costsb.   Development costsc.   Seats (military seats can cost upward of $100,000 per unit)d.   Periodic maintenancee.   Replacement partsf.   Maintenance crew training/explosive certification8.   Minimal time of use  The Ejection Site - Discussion of Airliner Ejection Seats.docx Discussion:   Ejection seats are complex devices which when used in military service have proven to be quitesuccessful at saving the lives of aircrew. As complex devices they require much maintenance andtraining to function with a high degree of success. Even though modern ejection seats are designedfor fully automatic function after initiation, the occupant requires training to use the seateffectively and safely. Ejection seats are designed to cause an occupant to separate from theaircraft at a high enough rate of speed to clear any part of the aircraft structure. Thisrequirement necessitates a high impulse force to be used to launch the seat and its occupant.Military seats are fired with an impulse in the Z axis of between 12 and 22Gz depending on theseat design. This impulse varies with the type of seat propulsion with the rocket/catapult seatbeing the lower value, and the pure gun type being the higher. This value, however, is alsoinfluenced by the weight of the occupant, and the values quoted above are based on a seatoccupant in the 150-200 lb weight range. With the continued influx of female pilots and crew,the weight of the average pilot is dropping. This is leading to much research to provide apropulsion system for an ejection seat that is usable over a much wider range of occupant weight.Other considerations include the occupant's connection to the seat. Parachutes require more thanjust a simple lap belt. At a minimum, the harness requirements include a pair of leg straps, a pairof shoulder straps and a chest strap. These straps must be adjusted for each individual to be asnug (read uncomfortable) fit for each passenger. In most airline trips I've been on, mostpassengers unbelt the minute the cockpit crew turn off the lab belt indicator (this is confirmed byrecent news stories about passenger injuries due to turbulence). In the case of a situation requiringa mass ejection, this would have to be delayed until ALL passengers AND crew are strapped insecurely prior to depressurizing the cabin, blowing the hatches and initiating ejection.When the cabin is depressurized and the hatches are jettisoned, the passengers would beexposed to the lower oxygen pressure in the upper atmosphere, the wind blast which would causeflail injuries and injuries by loose flying objects such as handbags, cameras, camcorders, trays,carry-on bags, and other objects.Jettisoning a large number of hatches in the roof of an airliner will also cause significant changesin the aerodynamics of the aircraft leading to control problems for the flight crew.The aircraft structure would require massive modification to make ejection seats feasible, includingstrengthening the cabin floor for the additional weight and the recoil of the seat firings. The cabinroof would have to be configured with the aforementioned hatches. The fuselage would thereforeneed a major increase in supports to allow it to hold its shape when the hatches were jettisoned.Overhead baggage compartments, and under-seat storage would have to be eliminated to giveadequate clearance above and, because of the seat depth, below. Legroom would have to beadjusted to make sure that adequate clearance was maintained on ejection to prevent leginjuries.  The Ejection Site - Discussion of Airliner Ejection Seats.docxMechanical ejection (spring/bungee) would provide inadequate thrust to ensure that passengerswould clear the empennage. Compressed gas systems that would have enough force wouldprovide too great of an initial force for safety. This means that pyrotechnic rocket/catapultsystems be used. These systems would necessitate significantly increased training for maintenancepersonnel, cabin and flight crews. The pyrotechnics would require maintenance on a regular basisin an explosive rated hanger with explosive rated storage.The ejection sequence would have to be from the rear to the front of the cabin, with the flightcrew being the last of all to be ejected. In an airliner with 30 rows of seats, the seats would haveto be jettisoned in row sets, with separation rockets to insure dispersal of the seats and preventmid-air seat collisions. There would have to be a delay between rows for the same reason. Thisdelay in military jets is in the vicinity of .4 to .5 second. This adds up to some 15-16 seconds for afull ejection of the aircraft. Seats that are unoccupied must be weighted to ensure that theyseparate in a predictable path. While the seats are firing, the aircraft would be exposed toforces from the catapult charges, and the center of gravity would be changing rapidly. This wouldcause significant difficulty to the flight control system to maintain stability.The above paragraph details one of the primary problems with airliner ejection systems. Themajority of airliner disasters occur at low altitude, usually during takeoff/landing which is asection of the airliner envelope that would not be conducive to a lengthy ejection sequence.Taking two examples: TWA Flight 800; and Sioux City: TWA 800's failure (regardless of thecause) occurred too fast for the flight crew to have initiated the ejection before the structuralfailure of the aircraft would have destroyed the firing system. If there was a cabin crew initiatedbackup, the structural failure might still have been great enough to have prevented the systemfrom functioning (presuming that the depressurization and wind blast conditions allowed the cabincrew to reach the actuation device and fire the system). Flight 800 also had an in-flight fire whichwould have caused casualties, and flying debris from the damage to the front of the aircraftwhich would be impacting the ejecting passengers. The airflow pattern from such damage wouldalso affect the flight path of the ejection seats, probably causing mid-air collisions which wouldcause injuries and seat malfunctions.Sioux City's crash was one where a system failure had disabled the plane’s flight controls, but leftthe engine controls active. The plane was under pilot control for some time prior to the impact. Inthis case, the plane could have been controlled to altitude, the passengers strapped in, briefed onprocedure, and then command ejected. This assumes that the passengers would remain calm,return to their seats and strap in. The pilots would then have to attempt to maintain control of theaircraft while the seats ejected for 15 seconds behind them (if it doesn't seem like a long time, seta timer for 15 seconds, close your eyes and wait...). When it finally got to the cockpit area, theflight controls would have to be ejected with the crew as they would be unable to release thegrips before they would be injured by them during ejection.
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