South African investigators have concluded that the unwise decision by a Boeing 737-200 captain to reverse in the dark, without guidance, led the jet to topple over an embankment and suffer substantial damage.

The crew had been preparing to ferry the aircraft (ZS-SGX) back to Johannesburg from the Hoedspruit airfield, following a charter service.

It had been cleared to head for Runway 18 by travelling north along the parallel taxiway A, and turning right on taxiway C. Visibility was poor and there was intermittent rain, said the South African Civil Aviation Authority, and the 737 had its taxi and landing lights on.

But the investigators, in an update to the inquiry, state that the crew switched off the landing lights momentarily in order to avoid dazzling an inbound aircraft on final approach.

When they turned the lights on again, the crew realised they had passed by taxiway C and reached the dead-end of taxiway A where, the SACAA says, there was "insufficient space to turn around".

The 66-year old captain - who had logged over 26,500h - opted to perform a 180° turn by steering the 737 into an area leading to hangars and then reversing.

"This was to be done without external guidance," says the inquiry into the 10 January 2011 accident, because the crew had established there were no maintenance engineers to assist.

While reversing the pilot "failed to stop [the aircraft] in time", it adds, and its main landing-gear rolled off the edge of the taxiway, causing the jet to slip down a steep 4m (13ft) incline into thorn trees.

"The captain attempted to power the aircraft out but was unsuccessful as the angle of the embankment was too steep," says the SACAA.

Although the nose-gear remained on the taxiway the 30-year old 737 sustained severe damage to its left Pratt & Whitney JT8D engine, as well as damage to its flaps, slats, ailerons, horizontal stabiliser and fuselage. The main landing-gear was also "subjected to unknown stresses" in the event, says the inquiry, but there were no injuries among the three crew members - the only occupants.

"It is the investigator's opinion that [before the accident] the aircraft should have been parked overnight [at the end of the taxiway] and help sought from ground crew or engineers the following day," it adds.

Source: Air Transport Intelligence news