South African investigators have determined that a Comair Boeing 737-800 departed Johannesburg despite uncertainty over a possible taxiing collision with a Mango aircraft.

The Mango 737-800, bound for Cape Town, had taken an incorrect taxiing route from the apron which resulted in its unintentionally following the Comair jet along taxiway A.

Taxiway A runs parallel to runway 21R and the Comair 737, heading for Durban, turned right onto the link N for an intersection departure.

The crew of the Mango aircraft, however, was planning a full-length take-off and needed to pass behind the Comair jet.

While the Mango pilots were offered the chance to steer briefly off taxiway A – via the G9 and G10 links – to give plenty of clearance, they opted instead to stay on the taxiway while passing.

But as it passed, its right-hand winglet contacted the left-hand horizontal stabiliser of the Comair aircraft, prompting the Comair crew to contact the tower.

"When Mango passed behind us we felt a bit of a bang," the pilot stated. "I am not sure if they touched us. Can you find out if they also felt anything?"

The Mango crew assured that they had not noticed any bump, before advising ground control that they had not taken the side-step route offered when passing the Comair jet.

Upon hearing that the Mango crew had not sensed any contact, the Comair crew appeared satisfied. "If he is sure he was clear, it might have been a wind gust as well, it could have been that," they told the tower. "If he is sure that he did not connect we are happy to go."

The tower again relayed that the Mango crew "didn't feel anything" and proceeded to discuss departure information with the Comair pilots.

But some 3min after initially stating that they had not felt any bump, the Mango crew indicated uncertainty about the situation and contacted ground control, saying: "Perhaps we should taxi to the bay and check it out."

This suggestion was transmitted nearly 1min before the Comair aircraft was cleared for take-off from runway 21R, according to the South African Civil Aviation Authority transcript of the 19 April incident.

But by the time ground control came back to the Mango crew the Comair aircraft was already outbound.

"The Comair is departing now," the Mango crew was told. "If you say that nothing happened and you are happy to go, you are more than welcome to go, but if you want to return we can organise that as well."

Doubts over the situation were sufficient for the Mango crew to decide to taxi back and check the aircraft. Inspection subsequently found scratch damage to the winglet showing it had "clipped" the other jet, says a preliminary inquiry document.

While the Comair 737 operated normally during flight, its crew was advised on approach to Durban of the damage to the Mango aircraft. The Comair jet underwent examination at Durban and ground personnel noticed that the left aft tip of the horizontal stabiliser as well as a static wick on the left elevator were bent.

Investigators have yet to reach final conclusions over the incident which involved aircraft ZS-ZWV, with 138 occupants, and ZS-SJH with 189. None of those on board was injured.