Poor signage and taxiway lighting at Johannesburg contributed to a British Airways Boeing 747-400 crew’s inadvertently following a narrow taxiway before the jet’s wing sliced into a service building.

But the inquiry into the accident, which demolished part of the building and led to the 747’s being written off, also points out that the pilots did not brief the taxi route and were unaware of a caution note in the aerodrome chart warning of potential confusion risks.

South Africa’s civil aviation authority states that the pilots suffered “loss of situational awareness” while taxiing in darkness for runway 03L ahead of departing for London Heathrow on 22 December 2013.

The crew had expected the aircraft to be facing north after pushback and had discussed a taxi route which would take the 747 out of the apron area, before turning south along taxiway A – which ran parallel and adjacent to the runway.

But the pushback clearance instead told the crew to face south. While this instruction was normal, the crew had not expected it, and queried the clearance among themselves before confirming it with air traffic control.

After engine start, the crew was cleared to proceed along a different taxi route, following taxiway B. Taxiway B took the aircraft south, out of the apron, but after 600m it crucially curved to the left at a junction. Not following this curve, but continuing straight ahead, would take the aircraft along the narrow taxiway M with buildings in close proximity.

Despite the different taxiing instruction the pilots “did not alter their expectation and review the new route”, says the South African CAA, adding: “If they had, they might have foreseen the conditions on [taxiway B].”

It states that a review might have resulted in the crew’s discussing the critical curve at the junction and prepared them to look for cues.

But the inquiry also determined that signage at the junction where taxiways B and M diverged was not adequate to warn crews. Some taxiway B centreline lights had not been functioning, it adds, while continuous blue edge lights feeding into taxiway M added to a “false perception” by the captain that the aircraft was still on taxiway B.

Some 10s before the collision the first officer, who was handling the aircraft, expressed concern about the width of the taxiway. The 747 was travelling at 14.5kt when its starboard wing carved into the BidAir Services building, injuring four employees.

Although Johannesburg’s advanced surface-movement system detected the aircraft’s encroachment onto taxiway M, it had not been fully commissioned and monitoring was “solely at [air traffic controller] discretion”, says the inquiry.

Around 1,000kg of fuel spilled from the 747’s tanks, British Airways estimated, although the investigation was unable to calculate a conclusive figure. None of its occupants was injured.

The aircraft (G-BNLL) sustained extensive damage to its wing and was subsequently parked and broken up.

South Africa’s CAA points out that the circumstances were similar to those of an incident involving another British Airways 747-400 (G-BYGA) at the same airport in April 2005. The crew had entered the narrow taxiway M after becoming confused by unclear markings and the aircraft, unable to manoeuvre, had to be pushed out.

Source: Cirium Dashboard