On 27 July 2010, a Boeing 737-800 being operated by South African Airways on a scheduled passenger flight from Johannesburg to Cape Town which was on the take off roll from an intermediate runway entry point on runway 21R and a Boeing 737-400 being operated by Comair on a scheduled passenger flight from Cape Town to Johannesburg which had just landed and was crossing the same runway further down were involved, in normal day visibility conditions, in a conflict which presented a high risk of ground collision. This risk was averted by a high speed rejected take off after ATC cancelled the take off clearance. None of the respective 130 and 123 occupants were injured.
An Investigation was carried out by the South African CAA AIID but its commencement was delayed as a result of poor process at the AAID.
It was noted that at the time of the event, the traffic situation was quiet and the weather conditions benign. The departing aircraft had been given a take off clearance whilst taxiing towards the intended intermediate runway entrance point and whilst still a significant distance from it. The arriving aircraft had just landed on the parallel runway and needed to cross the runway being used by the departing aircraft at a later intermediate point in order to reach its allocated parking gate.
Prior to reaching the runway crossing point, the arriving aircraft had been transferred to the responsible runway controller and had then received a crossing clearance just over a minute after the take off clearance had been given to the other aircraft. As the crossing point was approached, the corresponding stop bar was seen on red and the aircraft stopped. Upon querying the stop bar status with ATC, the bar was switched off and the instruction to continue was re-iterated.
It was noted that both aircraft had been on the frequency when their respective runway clearances had been given but had assumed that appropriate ATC instructions had prevailed. In the case of the departing aircraft, a rolling take off had been commenced upon entering the runway and the flight crew “did not pay attention to the radio broadcast between ATC and (the crossing aircraft)” which gave the latter crossing clearance. The flight crew of the arriving aircraft, although they were aware of the take off clearance given to the departing aircraft, “had not said anything to ATC about their concern regarding being cleared to cross the runway, while the other aircraft was cleared to takeoff from the same runway”. It was concluded that both flight crews “were confirmation biased that ATC had the situation under control”.
It was found that the departing aircraft had reached a speed in excess of 80 knots and travelled 1000 metres down the runway when ATC cancelled the take of clearance. The response had been prompt and after reaching a maximum speed of 101 knots, the aircraft had slowed to taxi speed by approximately 1000 metres further on, which was about 1000 metres before the position at which the other aircraft was crossing the runway.
The relative positions of the two aircraft (taken from the Official Report)
The Investigation noted that stop bars were installed at all runway and taxiway intersections and at the time were subject to a requirement that “no crossing of red stop bar lights will be allowed unless specifically approved by ATC and accompanied by a leader vehicle”. It was found that the ANSP Station Standard Instructions (SSI) for the operation of the stop bars were as follows:
- The stop bars must be operated on a 24/7 basis. The controller (effecting) the crossing clearance is also responsible for the operation of the relevant stop bar.
- Controllers are to ensure that all stop bars are correctly activated prior to clearances being issued.
It was noted that the TWR position involved in the issue of the conflicting clearances was being operated by a trainee and an OJTI and found that, in the weeks leading up to the investigated event, the trainee had been consistently recorded as performing below acceptable standards.
The Probable Cause of the Serious Incident was determined by the Investigation to be “rejected takeoff due to runway incursion” with Contributory Factors being:
- the error caused by ATC when giving instructions to one aircraft whilst taxiing to cross the active runway, after takeoff clearance was given to another aircraft using the same runway.
- the early takeoff clearance given to (the Boeing 737-800) , while still taxiing on taxiway “A” to RWY 21R holding point.
- the early crossing instruction given to (the Boeing 737-400) while still taxiing on taxiway “L” to RWY 21R holding point.
- the situational awareness (ability to keep track of the prioritised significant events and conditions in the environment of the subject) did not allow the ATC – Tower West to immediately detect the error.
- the ATC (Tower West) controllers (instructor and student) became complacent due to a sense of security, over-confidence and a perceived absence of threat resulting in inattention, due to the undemanding environment on the day.
Five Safety Recommendations were made as a result of the Investigation:
- that the Director of Civil Aviation (DCA) through the relevant department/division develop a requirement that ATNS should institute mandatory, recurrent, proficiency training related to reducing runway incursions for all controllers in high-fidelity tower simulators.
- that the Director of Civil Aviation (DCA) through the relevant department/division develop a requirement that Airlines/Operators and ATNS should increase training on runway crossing instructions and/or procedures.
- that the Director of Civil Aviation (DCA) through the relevant department/division develop a requirement that ATNS should develop (if not already existing) or amend the current Station Standard Instructions (SSI) to include an Air Traffic Control Resource Management (ATCRM) programme for aerodromes where coordination between two or more sectors exists.
- that the Director of Civil Aviation (DCA) through the relevant department/division develop a requirement that ATNS should change their procedures to give guidance to controllers regarding the minimum time interval/estimated distances from the runway holding point where takeoff and crossing clearances may be issued.
- that the Director of Civil Aviation (DCA) through the relevant department / division should define standard data requirements and standard data analysis methodologies for reports of events that may be classified as runway incursions in the Republic.
The Final Report of the Investigation was published in August 2012.