Introduction: Current air force training dictates that ejectees from high-performance aircraft mitigate landing injury hazards by letting the survival equipment in their seat packs fall to the end of an 8 metre lanyard while they are still descending under parachute. The exception is when they will land in trees and are told to retain the seat pack for the protection it offers against tree branches. Proposed automated seat pack deployment systems would protect aircrew from the landing injuries frequently seen when circumstances prevent them from deploying it manually, though this would also deny the option to retain the seat pack for tree landings. On the recommendation of the Board of Inquiry into the crash of CT155215, the special projects officer for aviation life support equipment at 1 Canadian Air Division Headquarters requested a study to review Canadian Forces (CF) ejection experience in order to validate the retention of seat packs for tree landings and to inform decisions on the adoption of automated seat pack deployment systems.
Results: A review of aeromedical literature showed that ground landing most often results in minor or no injuries. Minor injuries are most often to the lower extremities, though they are sometimes major and can involve the spine. Seat pack retention is a widely recognised risk factor for major leg and spinal injuries, though its role in aggravating or mitigating tree landing injury is not addressed in the literature. British aeromedical staff found injury data inconclusive on whether seat packs were better retained or deployed when landing in trees, though most British fleets are capable of automated seat pack deployment.
A review of 66 Canadian Forces ejections into trees with known seat pack statuses and landing injury profiles failed to find any evidence that seat pack retention into trees mitigates and prevents more injuries than it aggravates or causes. In fact, all central tendency measures of tree landing outcomes were better for deployed than for retained seat packs, although a Mann-Whitney U test showed deployed seat packs better at only an 80% confidence level (p = 0.2).
Significance: This result removes the justification for the tree landing exception to advice to deploy seat packs before landing, potentially simplifying best practise. It also indicates the value of wider fleet use of automated seat pack deployment systems to mitigate landing injury risks in other landing environments whenever ejectees lack the descent time or capacity needed to deploy their own seat pack. The Aviation Life Support Equipment Manual should also be changed to reflect these results.
Follow-up questions: Issues needing impact assessment and possible mitigation include wind-induced lanyard swing with automatic deployment at higher altitudes, the dynamics of ejectee suspension by lanyard when deployed seat packs snag in branches, and the optimal use of lanyard release in tree landings.
