Stored Hydraulic Energy in the Gear Bay — The System Was "Off"

A landing gear and its hydraulics store energy long after shutdown — charged accumulators, pressurized struts, and the sheer weight of the aircraft held by locks and pins. At Heathrow in 2021, an engineer troubleshooting nose-gear-door faults on a Boeing 787 pressurized the hydraulics and selected the gear lever with the downlock pins believed fitted — but the nose-gear pin had been inserted into the wrong bore of the downlock link. The nose gear retracted and the aircraft's nose struck the ground, injuring two people. The same energy hides everywhere in the gear bay: in 1999 a ground engineer at Manchester took a spray of pressurized hydraulic fluid to the skin and eyes when a DHC-8 nose gear collapsed during a fluid-transfer operation.

This is the aviation twin of lockout/tagout: the hazard regulators wrote the stored-energy rule for. OSHA 29 CFR 1910.147(d)(5) requires that all potentially hazardous stored or residual energy be relieved, restrained, and rendered safe before work — and the gear bay is where aviation maintenance meets it daily. It is also the first card destined to become a playable EON Live mission: the conditional procedure — isolate, ask "is stored pressure still present?", bleed, verify, only then proceed — is exactly the branching a scripted trainer cannot do.

1. Isolate and tag hydraulic power to the system you are working — all sources, not just the pumps.
2. Ask the conditional question — is stored pressure still present? Accumulators and struts hold energy after shutdown.
3. Bleed stored pressure down and re-check; repeat until the gauge reads zero.
4. Verify zero energy at the gauge, and fit the correct pins in the correct bores — physically confirm engagement, never assume from paperwork.
5. Only then proceed. Anything abnormal — stop and escalate.

Aviation-specific rates for stored-hydraulic-energy injuries are not quantified in public sources — but the hazard class is recognized enough that the control-of-hazardous-energy regulation names hydraulic energy explicitly, and gear-bay events keep appearing in AAIB bulletins.

Uncommanded gear retraction on the ground — the aircraft comes down on structure and anyone under it; high-pressure fluid injection and spray injuries; crush injuries at the downlock linkages. At Heathrow: significant airframe damage and two minor injuries (AAIB Bulletin 12/2022). At Manchester: the engineer needed treatment for hydraulic-fluid contamination of skin and eyes (AAIB Bulletin 2/2000).