Simple mistakes while entering flight management system data led a LOT Boeing 737-500 to fly a circuitous route over northwest London last year, as instrument and language problems left the crew struggling to navigate the jet.
Limited command of English by the Polish aircraft’s crew aggravated a situation which arose after an oversight during preparations for a London Heathrow-Warsaw service on 4 June 2007.
On stand the co-pilot punched incorrect co-ordinate information into the computer while realigning the inertial reference systems. By entering the longitude as ‘east’ instead of ‘west’ – possibly because few LOT destinations are west of zero longitude – the co-pilot erroneously gave the aircraft’s position as 33.5nm from its actual location.
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The UK Air Accidents Investigation Branch (AAIB) says that this “fairly simple” mistake led directly to the “serious” incident which followed.
Although the crew claims there was no second attempt to realign the inertial reference systems after the aircraft had started taxiing, there is evidence that such an attempt was made while the 737 was holding for take-off. The AAIB believes the aircraft departed without this procedure having been correctly completed, and the flight management system subsequently failed to update the aircraft’s position.
Almost immediately after take-off the crew noticed that hardly any information had appeared on their electronic attitude director and horizontal situation indicators, the two main displays in front of the pilots’ control yokes. The crew had to resort to using standby instruments and advised air traffic control of navigation difficulties.
The flight was supposed to follow the BPK5J departure which tracks northeast to the Brookmans Park VOR. But the aircraft started flying north – coming into conflict with another aircraft – then northwest, then west, despite air traffic control instructions to fly a 050° heading.
“At this stage there were a number of exchanges between [the flight] and the controller in which it was apparent that the commander, who was making the radio calls, was not able to understand some of the instructions,” says the AAIB.
“Quality of the transmission signal was good but a number of the exchanges were misunderstood, probably as a result of language difficulties.”
After being asked to make a 180° right turn, the pilot instead read back “turn right 19°”, and shortly afterwards informed the controller that the aircraft’s heading was 330° when it was actually 030°.
At no time did the crew declare an emergency. The pilots, increasingly dependent on air traffic control for position information and navigation, opted to return to Heathrow and controllers tried to vector the aircraft towards the west.
“Altitude and speed were complied with but the aircraft continued to respond to heading instructions slowly and erratically,” say the investigators. After passing the airport the 737 turned south, cutting across the localiser path for runway 09L, before turning north and cutting through it again.
Controllers gave ‘start and stop’ turn instructions to align the aircraft with runway 09L and cleared the 737 for a visual approach. It landed safely, although at one point appeared to be heading for the other parallel runway, 09R, which was cleared as a precaution.
“This incident demonstrates how reliant pilots may become on the flight management system, and how essential it is to ensure that the system is provided with accurate data,” says the AAIB, which adds that better cross-checking would have prevented the situation from developing.
But it has not issued any safety recommendations because the carrier is considering reminding pilots to take care when manually entering co-ordinates into aircraft systems. The airline is also looking at revising training to highlight the benefits of declaring an emergency under certain circumstances.
ICAO originally set a March 2008 deadline for international pilots to reach a required minimum level of proficiency in the English language. Poland’s civil aviation authority, says the AAIB, is due to specify a compliance date. ICAO is seeking full implementation by March 2011.
Source: Air Transport Intelligence news
Source: Flight International
