The Wrong Bolts — Windscreen Blowout at 17,300 Feet

A BAC One-Eleven's left windscreen was replaced overnight by the Shift Maintenance Manager working alone. He selected the securing bolts by matching them to the old ones by touch and eye at an uncontrolled parts carousel in poor light, instead of looking up the part number. 84 of the 90 bolts he fitted were 0.026 inch too small in diameter, and 6 were 0.1 inch too short. On the next morning's passenger flight, as cabin pressure built, the windscreen blew out of its frame — and the commander was sucked halfway out of the aircraft. Cabin crew held him by the legs until the copilot landed at Southampton. He survived.

A safety-critical task was done by one person who also certified his own work — the AAIB's first causal factor. The windscreen was not designated a "Vital Point," so no independent check was required, and the installation's first real test was a pressurized passenger flight. The fix the industry drew from this: duplicate inspection of safety-critical work, controlled parts stores, and never certifying your own critical task — pillars of today's Part-145 human-factors requirements.

1. Identify the fastener by part number from the Illustrated Parts Catalogue — never by eye-matching the old bolt.
2. Draw stock from the controlled, labeled store; an unlabeled carousel is not a source of aircraft parts.
3. Install and torque to the maintenance manual, with adequate lighting and the right access equipment.
4. Safety-critical work gets an independent (duplicate) inspection before certification — never self-certified.
5. Prove the installation before it carries passengers — the first pressurization must not happen on a revenue flight.

Frequency of this exact failure is not quantified in public sources — but incorrect installation of components sits at the top of the industry's recurring maintenance-error listings (UK CAA / Boeing MEDA canon; exact citation locked at the corpus gate).

The left windscreen departed at 17,300 feet; explosive decompression; the commander was partially ejected and pinned against the airframe for over 20 minutes while cabin crew restrained him by the legs. Serious injuries to the commander (fractures to the right arm and wrist, broken left thumb, bruising, frostbite, shock), minor injuries to one steward. Zero fatalities; the aircraft landed safely at Southampton (AAIB AAR 1/92).