Freight operator TNT Airways is taking precautions to protect auxiliary power units at Istanbul after establishing that birds have been blocking the exhaust ducts of its Boeing 737 freighters.

It follows an incident last month when air traffic controllers at Istanbul Ataturk airport notified the crew of a 737-300 (OO-TNF) that smoke was being emitted at its tail during start-up for a flight to Liege in Belgium.

Engineers from maintenance firm Turkish Technic found metallic parts, including scissors, lancets and springs, some of them burned and scorched, in the APU exhaust.

The jet departed late, leaving authorities questioning whether the aircraft had been vandalised or sabotaged, until later in the week another TNT 737 arrived and parked in the same area. Staff monitoring the aircraft noticed birds frequently flying over to the 737 and dropping metal objects into the APU exhaust.

Turkish investigators have suggested the birds have been collecting debris left when a fire struck a cargo area of the airport in May last year. TNT has been parking its freighters near the normally unused fire-affected area because of capacity limitations at Ataturk. The airline is now putting covers on the APUs.

Source: Flight International