Swedish investigators believe pilot fatigue contributed to a Cathay Pacific Boeing 747-200 freighter's sustaining heavy engine damage after accidentally taxiing into its tow-tractor at Stockholm Arlanda last year.
The pilots had been awake for 18-20 hours by the time of the accident, which occurred early on 25 June just after the jet had been pushed back from stand R9 for a service to Dubai.
Investigation commission SHK has concluded that, shortly after the tow-tractor was disconnected from the nose-gear, the pilots started to taxi the aircraft before a ground technician had given an unambiguous all-clear signal. The Schopf 356 tractor had been moved a short distance but was out of the pilots' field of vision.
SHK says that, while the pilots read the normal checklist after engine start, it "did not contain any point" concerning a 'clear signal' - a specific thumb-up gesture showing that the aircraft is clear to taxi.
Only a supplemental note in the carrier's expanded checklist informed pilots that the ground dispatcher would "clearly display" to them the steering pin removed from the nose-gear.
The Arlanda tow-tractor driver, who was preparing to move the vehicle clear, hastily abandoned it when he heard the 747's engines powering up.
Both the driver and the ground technician "had to run in order to be safe" and the aircraft struck the tractor with its inboard left-hand Rolls-Royce RB211 engine. The rear of the vehicle penetrated the nacelle by 20-30cm, heavily damaging the cowling, pumps, fuel lines and control units, and the engine began leaking fuel.
In its report into the accident, which also badly damaged the tractor, SHK states that - despite the fuel leak, close to hot exhaust and electrical wiring - emergency services were not summoned for nearly an hour.
It attributes the collision to "inadequate" checklists for the crew regarding confirmation of an all-clear signal. But SHK also highlights the length of time the pilots had been awake and says the time of the accident, 03:33, was within a biological window of low activity. Stress and fatigue, it says, probably limited the crew's concentration abilities.
SHK identifies the 747-200F involved in the accident as being registered B-HIH. Flight's ACAS database shows that the jet, serial number 23120, is owned by Cathay Pacific.