Airbus A310 descends below cleared altitude due to incorrect altimeter setting

Casualties unknown • On approach to Birmingham Airport, GB

An Airbus A310 operating a passenger flight from Tehran to Birmingham descended significantly below its assigned altitude because the crew failed to update the altimeter to the local pressure setting.

What happened

On 24 November 2006, an Airbus A310, registration F-OJHH, was conducting a scheduled passenger flight from Tehran to Birmingham Airport. While being radar vectored for an ILS approach to Runway 15, the aircraft was cleared by the radar controller to descend from FL80 to 4,000 ft, and subsequently to 2,500 ft, based on a QNH of 982 hPa.

During the descent, the radar controller observed the aircraft continuing to descend below the permitted 2,500 ft level. The controller issued multiple instructions to climb and warned the crew of a television mast located 4 nm east of their position at an altitude of 1,358 ft. Upon questioning by the controller, the crew realized they had not updated their altimeter sub-scales from the standard pressure setting of 1013 hPa to the local Birmingham QNH of 982 hPa.

Following the correction of the altimeter setting, the crew initiated a climb and leveled off at 2,000 ft. The aircraft successfully intercepted the localiser and completed a normal landing with no injuries to the 84 passengers or 11 crew members on board.

The investigation

The investigation established that the crew had failed to implement the operator's Standard Operating Procedure (SOP) regarding altimeter settings during descent. According to the descent checklist, both the Pilot Flying (PF) and the Pilot Not Flying (PNF) are required to set the QNH when cleared by ATC to descend from a flight level to a specific altitude.

Because the altimeter remained set to 1013 hPa instead of 982 hPa, a discrepancy of approximately 930 ft existed between the aircraft's actual altitude and the altitude indicated on the flight deck instruments. Consequently, when the instruments indicated the aircraft was at 2,500 ft, it had actually descended to an altitude of approximately 1,570 ft.

Findings

  • The crew did not change the altimeter setting from the standard 1013 hPa to the local Birmingham QNH of 982 hPa during the descent.
  • The failure to update the altimeter sub-scales resulted in the aircraft descending to an actual altitude of 1,570 ft while the instruments indicated 2,500 ft.
  • The crew reported no specific distractions or unusual flight deck activities that would have prevented the adjustment of the altimeter settings.

Probable cause

The primary cause of the altitude deviation was the crew's failure to adjust the altimeter setting from the standard pressure of 1013 hPa to the local Birmingham QNH of 982 hPa during the descent.

Frequently asked questions

What happened in the 2006-11-24 Airbus S310 accident near On approach to Birmingham Airport, GB?

An Airbus A310 operating a passenger flight from Tehran to Birmingham descended significantly below its assigned altitude because the crew failed to update the altimeter to the local pressure setting.

What aircraft was involved and where did it happen?

The accident on 2006-11-24 involved a Airbus S310, registration F-OJHH, at On approach to Birmingham Airport, GB.

What was the probable cause of the accident?

The primary cause of the altitude deviation was the crew's failure to adjust the altimeter setting from the standard pressure of 1013 hPa to the local Birmingham QNH of 982 hPa during the descent.

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