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11th of December 1990

Updated: Dec 11, 2021

An Air Canada Flight 866 was on route from Montreal Canada to London Heathrow, England on this day in aviation history in 1990. With approximately 30 minutes to go before landing the crew of the Lockheed Tristar, C-GAGI (s/n `1209), was busy setting the aircraft up for the descent from FL370. When a rapid loss of cabin pressure occurred.

C-GAGI in approach configuration (not the incident flight)


The crew did not hear any noise but noticed a change in cabin pressure, the commander later stated that he felt his ears pop. After seeing the first officer (f/0) donning his oxygen mask he handed over control to the f/o shortly to allow him to put on his own oxygen mask. While the cabin altitude warning sounded the EMERGENCY DESCENT CHECKLIST was called for;

  • Cabin Signs - ON

  • Continuous Ignition - ON

  • Throttles - IDLE

  • Speedbrakes - EXTEND

  • Accelerate to - Vmo - Mmo

The second officer also put on his mask and continued the EMERGENCY DESCENT CHECKLIST in an attempt to control the cabin altitude rate of climb. He didn't succeed, the Cabin Rate of Climb remained at the maximum indication. The first officer made an announcement to the cabin, saying; "ATTENTION PUT ON YOUR OXYGEN MASKS IMMEDIATELY. In the rear of the cabin, two cabin attendants heard a loud sound and the rushing sound of air from the left rear toilet. They attempted to open the toilet door but were unable to do so. The oxygen masks began to dropdown. In the first-class cabin, the purser saw the masks drop as well and after donning a mask herself made announcements to instruct the passengers.


1An Air Canada Flight 866 was on route from Montreal Canada to London Heathrow, England on this day in aviation history in 1990. With approximately 30 minutes to go before landing the crew of the Lockheed Tristar, C-GAGI (s/n `1209), was busy setting the aircraft up for the descent from FL370. When a rapid loss of cabin pressure occurred.

The emergency descent brought the aircraft down to FL310 when the First Officer declared emergency stating they had a rapid decompression and were in an emergency descent. Cabin altitude peaked a little later at 20.600 feet (data from FDR), from that point the cabin altitude and aircraft altitude remained near identical. During the Emergency Descent airspeed peaked at 377 knots with a maximum vertical speed of 8500 feet per minute. 5 minutes and 20 seconds after the loss of pressurization the aircraft levelled off at 10.00o feet.

With the aircraft at 10.000 feet the Cabin Service Director (CSD was called to the flight deck, where he told the commander what they heard from the left rear toilet area. A check of the passenger revealed that on;y 3 passengers had severe head- and earache. The flight continued to London Heathrow Airport where a normal approach and landing was made. After parking, the aircraft was med by medical staff to check the injured passengers.

Drawing of the rear pressure bulkhead and location of the crack (© AAIB UK)

An investigation was launched and a rupture in the rear pressure bulkhead, adjacent to the rear left toilet was found, with the toilet walls (partly displaced in that area) Detailed analysis of the cracked area revealed that the crack had started at Score (Groove) on the aft face of the rear pressure bulkhead. It was later determined that the score was the result of the work performed during the manufacturing of the aircraft. It became clear that it was caused by a metal tool, most probably done to remove excess sealant. Other aircraft were found with similar score damage at the same location as the result of AD's being issued by the FAA and Transport Canada.

The full report on this incident with more details about the failure and the cause can be found by clicking here.



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