Investigators have concluded that a Mahan Air Airbus A310-300 crew's failure to set their altimeter to local pressure led to the twinjet descending far below its cleared altitude during an approach last year to Birmingham International Airport in the UK.
The incident on 24 November happened nine months after another Mahan Air A310, also approaching Birmingham, descended to an extremely low altitude while still a long distance from the runway. Investigators have yet to conclude their inquiry into that incident.
The inquiry into the November 2006 event has discovered that the Iranian-operated aircraft had been cleared to 2,500ft (760m) as it arrived from Tehran. Instead of keeping to this height, the A310 continued to lose altitude even after air traffic control contacted the aircraft three times to alert the pilots. The presence of a tall mast in the vicinity then led the controller to order the A310 to perform an immediate climb.
The crew had not reset the altimeter from the standard pressure setting of 1013hPa to the local figure of 982hPa - a difference of 31hPa that would have led to a 930ft error in the altimeter reading.
In a bulletin, the Air Accidents Investigation Branch says: "The crew could not recall any distractions or unusual flightdeck activity at the point at which they would normally have adjusted the altimeter sub-scales." After being warned about the mast and following a query from the controller, the A310 crew realised the altimeter pressure setting was incorrect.
A mis-set altimeter was to blame for the A310 descending too low
Source: Flight International