British Airways A321 near London on Dec 20th 2011, both flight crew nearly passed out

Last Update: October 11, 2012 / 12:55:17 GMT/Zulu time

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Incident Facts

Date of incident
Dec 20, 2011

Classification
Incident

Airline
British Airways

Aircraft Type
Airbus A321

ICAO Type Designator
A321

The British AAIB released their Bulletin concluding the probable cause of the incident was:

The symptoms experienced by the commander may have been the result of the after-effects of a cold, combined with coincidental head and aircraft movement. The temporary symptoms experienced by the co-pilot may have been a reflection of the potentially evolving situation of an incapacitation at an early stage in the flight leading to possible mild hyperventilation.

Their subsequent actions were taken in view of this perceived potential for incapacitation. No aircraft faults were discovered and no other aircraft occupants were affected by any symptoms. The crew did not require medical treatment and resumed flying duties without any recurrence of their earlier symptoms.

A previously unknown intermittent fault with the CVR was identified and this has resulted in a Safety Recommendation.

The AAIB reported that the captain (44, ATPL, 8,570 hours total, 3,445 hours on type) as well as the first officer were well rested, neither of them had flown the day before. The pilots met prior to the incident flight about 15 minutes before begin of check in, preflight preparations were normal and the aircraft departed from runway 27R. While climbing through FL120 the captain looked down onto the center pedestal to change a radio frequence at a time when the aircraft began to roll out of a 25 degrees bank and the pitch attitude was increasing by 4 degrees, when she began to feel slightly dizzy and light headed. The dizziness did not abate, at FL210 she asked the first officer whether she felt well, which the first officer affirmed at first but then indicated she was feeling light headed. Both crew therefore donned their oxygen masks, and the first officer levelled the aircraft. The crew decided to return to Heathrow and after initially being assigned runway 27L landed safely on runway 27R.

After vacating the runway the crew removed their oxygen masks, but donned them again after some light headiness returned. After the aircraft had reached the parking position, they removed the oxygen masks again, this time with no ill effects.

Shortly after the aircraft arrived on stand emergency services boarded the aircraft and examined cabin and cockpit air with no smoke or fumes detected. Paramedics checked both pilots with no abnormal symptoms. No further medical treatment was required, a check the following day did not reveal any necessity for medical care, both flight crew therefore were not seen by a doctor.

The captain had suffered from a cold, but felt fit to fly and had not taken any medication in the 48 hours prior to the flight. The first officer reported in her 12 years of flying experience she had not experienced such symptoms before. There was no recurrence of the symptoms with either flight crew.

During the entire flight there had been no indication of any aircraft system anomaly, the cabin altitude had reached a maximum of 3,200 feet. Both pilots were not aware of any smells, fumes or smoke, none of cabin crew or passengers experienced any abnormal effects.

Examination of the aircraft revealed a malfunction of the cockpit voice recorder prompting the vast majority of the bulletin to be dedicated to the technicalities of that fault.

The AAIB also looked into the cabin air supply stating that air taken from the bleed air outputs of each engine was passed through an air conditioning system. The outputs of both air conditioning systems is then sent to a single mixer unit before being distributed to the three cabin zones, the temperature of each of which is independently controlled by mixing unconditioned hot air into the conditioned air. The unconditioned hot air is taken from "a combined single supply of hot air that is taken from the inlet for each pack".

The AAIB analysed that the both pilots continued to execute their pilot duties properly throughout the event, neither one was incapacitated. The coincidence of the captain moving her head to look down onto the center console together with the aircraft movement to level wings following a 25 degrees bank and increasing the pitch attitude by 4 degrees may have caused a "disorientation episode caused by a combination of oculogyric disorientation and an alternobaric episode made more likely by the lingering effects of a cold. The resulting natural instinct to hyperventilation could lead
to hypocapnia which may well have contributed to the feeling of light-headedness."

The AAIB continued: "The onset and clearance of the co-pilotÂ’s symptoms within approximately 25 seconds may have been a reflection of the potentially evolving situation of crew incapacitation at an early stage in the flight leading to mild hyperventilation." and concluded the analysis: "The reason for the dizziness experienced by both pilots when they first removed their oxygen masks on the ground could not be positively determined but it is possible that it was caused by the effect of a sudden reduction in inspired oxygen concentration on cerebral oxygenation, blood flow and pressure."
Incident Facts

Date of incident
Dec 20, 2011

Classification
Incident

Airline
British Airways

Aircraft Type
Airbus A321

ICAO Type Designator
A321

This article is published under license from Avherald.com. © of text by Avherald.com.
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