On 24 September 2015, a Boeing 737-400 (AP-BJR) being operated by Shaheen Air International on a passenger flight from Sharjah to Bacha Khan (Peshawar), Pakistan as SAI 791 began it's normal visibility night take-off from the taxiway parallel to the runway for which take-off clearance had been given. No obstructions were encountered and the taxiway was sufficiently long to allow the take-off to be successfully completed after ATC decided not to intervene.
An Investigation was carried out by the UAE GCAA Air Accident Investigation Sector (AAIS) but there was a four day delay in the initial notification of the event to the AAIS. CVR data relevant to the event had not been preserved, although DFDR data was made available by the aircraft operator when requested. It was found that the statements provided by the air traffic controllers involved could not be supported by any relevant recordings and the flight crew maintained in their statements that their take-off had been made as cleared from the runway. Also, since the GPS position data recorded by the DFDR was derived data, it could not be used to determine the ground track of the aircraft, which was instead achieved by synchronising radio transmissions made by ATC and the aircraft with other recorded flight data.
It was found that the 44 year-old Captain had 4,079 hours total flying experience including 1,235 hours on type and had been acting as PF for the investigated departure. He was accompanied by a 39 year-old First Officer who had 1,049 total flying hours of which 182 hours were on type. A third type rated ATPL pilot was also present in the flight deck. He had 3,165 hours total flying experience including 388 hours on type and his status was described by the aircraft operator as "responsible for monitoring all activities in the cockpit". It was noted that this same "Observer Pilot" had also flown as an Observer with the same Captain on two sectors the day before the investigated flight. The TWR controller involved had "several years’ experience" at the Sharjah TWR and she was on duty for the first night shift of a five day duty cycle which had commenced five hours prior to the occurrence under investigation.
It was established that the aircraft had taxied for departure after approximately a one hour turnround. The taxi and take-off occurred in good visibility without moonlight. Two controllers were on duty in the TWR, one of whom was the Supervisor. Both controllers were present in the TWR at the time. The 'line' controller was operating both the GND and TWR positions, wearing a headset and standing. After pushback from the gate, the controller using the GND frequency, issued a clearance to "taxi to Alpha, Alpha two zero, holding point Bravo two zero, runway three zero" which was read back incompletely as "Alpha to holding point runway three zero” without challenge from the controller.
A change to TWR frequency was given and on checking in there, the First Officer advised that they would be "holding short of the runway three zero", which was acknowledged by TWR and, after a request to repeat this response was followed by the instruction from TWR to "hold short at Bravo two zero" to which the First Officer replied without challenge from the controller that they would "hold short of three zero”. Twenty seconds later, as the aircraft was about to turn left from taxiway 'A' onto taxiway 'A20' (see the first illustration below) the controller transmitted "cleared for take-off runway three zero, Bravo two zero without delay clear take-off, surface wind is one three zero degrees five knots bye bye” which was read back without challenge by the controller as "cleared for take-off runway three zero". The stop bar on B20 protecting runway access on the taxi route being taken was therefore switched off and a potential indication of the runway ahead which would have been visible to the crew as they approached what should have been the crossing of the Bravo taxiway as they taxied from A20 ahead onto B20 (see the illustration below).
An annotated reconstruction of the aircraft ground track. [Reproduced from the Official Report]
As the aircraft taxied on 'A20', TWR then said "...keep your speed up until you've cleared the runway" to which an immediate request from the aircraft to "say again" was followed by TWR transmitting "....without delay cleared take-off runway three zero surface wind one three zero degrees five knots bye bye" acknowledged by the aircraft as "cleared for take-off runway three zero...". Within a few seconds, the aircraft had begun to turn left onto taxiway 'B' but as it did so, its taxi speed slowed and with the aircraft still not fully on the taxiway centreline, TWR transmitted "... expedite please I’ve got traffic turning final" (this traffic was at 7nm at this time). The instruction was immediately acknowledged and as the aircraft completed its alignment on taxiway 'B', the engines began to spool up and a rolling take-off commenced with the engines reaching take-off thrust and ground speed 69 KCAS as the aircraft passed taxiway 'A18' (see the illustration below). Both the controller in position and the Supervisor became aware that the aircraft had commenced its take-off on taxiway 'B' at this point. By the time it passed the 'B14' intersection, DFDR data showed that it had been accelerating through 128 KCAS. They jointly made the decision to allow the take-off to continue, aware that the remainder of taxiway 'B' was sterile and being unsure how near to rotation the aircraft was.
Part of the aerodrome layout - note that although the obstructed controller sight line when seated is annotated, the controller was standing at the time. [Reproduced from the Official Report]
Once the aircraft was airborne, the crew advised that they were changing to Dubai as required and the controller acknowledged this without informing the crew of their error. ATC did "not immediately advise" the aircraft operator either and the flight crew were not made aware of the event until five days later - after the event had been reported to the GCAA AAIS.
The flight crew subsequently stated that there had been "no doubt" during the take-off that they had been on runway 30 and the Captain stated that there had been "no pressure from the air traffic controller to depart".
The Investigation highlighted a number of relevant circumstantial factors in respect of the error made by the crew which included the following:
- The Jeppesen aerodrome chart used by the crew was a correct representation of the aerodrome layout.
- None of the three pilots on the flight deck noticed the clear differences between the lighting on taxiway 'B' and that which they would expect to see on an active runway.
- The Sharjah 'Aerodrome Manual' had not been updated since January 2013 - prior to the very significant changes made the following year on account of the construction and opening of the new runway.
- No 'Hot Spots' had been identified by the Aerodrome Operator after the inauguration of the new runway and the conversion of the old runway to an additional parallel taxiway designated as taxiway 'B'.
- The centreline of the runway was 250 metres from the centreline of Taxiway 'B'.
- The Aerodrome was not equipped with Surface Movement Radar (SMR) and the VCR was not equipped with aerodrome cameras and monitors.
- Taxiway designation prior to the opening of the new runway was mostly by use of a single letter. For the new runway layout, many taxiways were given alphanumeric designations - for example, 'G' became A20, 'F' became A18 and 'C' became A6.
- The displaced threshold markings of the former runway were still faintly visible through the painted area on taxiway 'B' and "signs of the previous runway imprint could be seen" (see the diagram below).
- The AIP stated that the taxiway was 25 metres wide. This width was the distance between the yellow-painted edge lines limiting the taxiway width to just part of the 45 metre paved surface of the former runway.
An aerial view of the painted threshold areas of taxiway 'B' and runway 30. [Reproduced from the Official Report]
- All taxiway centreline lights and lead-in lights to the runway were green. However, at night, there was a difference in the shade of green and the level of brightness used for the centreline lead-on lights from taxiway 'A20' to taxiway 'B' and the similar lights at the opposite end of the runway from all other green taxiway centreline lights,
- The two intermediate red stop bars at position 'BA' on the Bravo taxiway and in a similar position 'BG' at the opposite end of the taxiway had not been lit at any time during the night of the investigated event and there were no Standard Operating Procedures (SOPs) for their use.
- Air Traffic Services at Sharjah were provided by a contractor - Serco Middle East.
- Standard phraseology was not consistently used in communications between ATC and the aircraft prior to the unauthorised take-off.
- The failure of the flight crew - specifically the First Officer - to read back clearances as given was not challenged by the controller.
- Although the aircraft Captain had subsequently stated otherwise, it was considered that successive transmissions over a 43 second period that included the words “depart without delay”, “keep the speed up” and “expedite” could have influenced the flight crew in making the incorrect decision to turn and eventually take off from the taxiway.
- At night during a full length take-off from runway 30, the only available controller reference point to visually ascertain where an aircraft is situated on the runway was the red stop bar at taxiway 'B14'. The holding points at the marked runway entry positions for entry from taxiways 'B20' and 'B19' were neither lit nor visible from the TWR.
- A controller seated at either the GND or TWR positions, is prevented from seeing taxiway 'A20' and the lead-on to taxiway 'B' by one of the metal strips which separate the window panes.
- There was no mention in the Sharjah ATC procedures of one controller working both GND and TWR positions.
- The aircraft operator had not performed a risk assessment to ascertain whether the changes associated with the opening of the new runway had introduced any new threats which might affect either the performance of its pilots or the continued safe operation of its aircraft in any other way.
- Aircraft operator SOPs did not require flight crews to positively identify a take-off runway or specify what the "monitoring" duties of the Observer Pilot were.
- ICAO Annex 14 was noted to suggest that "Existing taxiways wider than recommended in this Annex, can be rectified by painting taxi side stripe markings to the recommended width".
- The Sharjah Operations Manual required that controllers should ensure that pilots involved in an incident requiring reporting action are aware of the incident and the consequent action.
- Timely reporting of the investigated event to the GCAA AAIA Duty Investigator did not occur.
It was noted that during the Investigation, an Airbus A320 had made a similar turn onto taxiway 'B' from 'A20' when cleared to depart from runway 30 but on this occasion, the TWR controller had noticed the error immediately and intervened before a take-off was commenced. Only after this incident were ATC procedures changed to require that the red stop bar at 'BG' on taxiway 'B' must be lit whenever an aircraft is departing runway 30 from taxiway 'A20'.
The Investigation reviewed some of the actual or attempted taxiway take-offs which had occurred at other airports and for which an independent Investigation Report had been published. These included attempted night taxiway take-offs by an Airbus A340 at Hong Kong in 2010 and by a Boeing 767 at Singapore in 2015 and an actual taxiway take-off in daylight by an Airbus A320 at Oslo in 2010.
The formal statement of Cause of the event was that "most probably, the flight crew did not devote sufficient attention to the taxi route, or taxi route lighting and signage" and that "the flight crew misunderstood the air traffic control instructions and failed to identify that the aircraft had been aligned on a taxiway, instead of on the runway, resulting in a take-off from the taxiway".
Eight Contributing Factors were also identified as follows:
- the Aircraft Operator Standard Operating Procedures (SOP) did not require verification by the crew that the aircraft is lined up on the correct runway before commencement of take-off;
- the early take-off clearance given by ATC when the Aircraft was approximately 200 metres away from runway 30 holding point;
- the urgency of the Air Traffic Controller for the Aircraft to depart;
- the red stop bar lights at the CAT II/III holding point for runway 30 was already OFF;
- the brighter green lead-on lights for taxiway Bravo were probably mistakenly interpreted as the lead-in lights for the runway;
- similar numeric descriptors for taxiway and runway designation;
- the Air Traffic Controller lost visual watch on the aircraft for some time;
- the possibility that the flight crew assumed that taxiway Bravo was the runway due to the width of the taxiway.
A total of 24 Safety Recommendations were made as a result of the Investigation as follows:
- that Shaheen Air International review training and procedures for flight crew members to ensure that the following are addressed: use of the current airport diagram not only during the planning phases, but also while taxiing; minimising cockpit tasks during taxi; observe “sterile cockpit” procedures; always practice a “heads-up, eyes out” mode while taxiing; read back accuracy; and always to verify the aircraft position before the take-off is commenced. [SR11/2017]
- that Shaheen Air International review and address flight crew performance regarding read back of air traffic control instructions. [SR12/2017]
- that Shaheen Air International issue checklist procedures to ensure that there is positive runway verification by all crew members before take-off is commenced. [SR13/2017]
- that Shaheen Air International re-emphasise the principles of CRM and enhance effective communication amongst flight crew members. [SR14/2017]
- that Shaheen Air International evaluate the potential benefits of the runway awareness advisory system (RAAS) for fitment on applicable aircraft. [SR15/2017]
- that Shaheen Air International define the cockpit duties of the third pilot, when assigned to a flight. This should also be included in crew resource management (CRM) training. [SR16/2017]
- that Sharjah Air Traffic Services - Serco Middle East re-emphasise to the controllers the use of standard phraseology as mentioned in GCAA CAAP 69, read back accuracy and the effective use of the runway holding points and intermediate holding point stop bars. [SR17/2017]
- that Sharjah Air Traffic Services - Serco Middle East re-emphasise to the controllers the responsibility of keeping a visual watch on the aircraft, and before issuing clearance for take-off, to verify that the aircraft is at the runway holding point. [SR18/2017]
- that Sharjah Air Traffic Services - Serco Middle East evaluate and mitigate the risk, and establish procedures, of allowing a single air traffic controller to assume the combined responsibilities of the Ground and Tower positions. [SR19/2017]
- that Sharjah Air Traffic Services - Serco Middle East review and implement procedures for the immediate notification of serious incidents and accidents to the Air Accident Investigation Sector (AAIS), the flight crew, and the concerned aircraft operator. [SR20/2017]
- that the Sharjah Department of Civil Aviation review and implement procedures for the immediate notification of serious incidents and accidents to the Air Accident Investigation Sector (AAIS). [SR21/2017]
- that the Sharjah Department of Civil Aviation re-assess and mitigate the risk associated with the use of similar designations for taxiways that lead to runway 12/30 that may cause taxiway confusion. [SR22/2017]
- that the Sharjah Department of Civil Aviation re-assess the risk associated with the green lead-on lights towards taxiway Bravo beyond taxiway Alpha 20 and taxiway Alpha 2. [SR23/2017]
- that the Sharjah Department of Civil Aviation review and determine whether the intersection of taxiway Alpha 20 with taxiway Bravo, and taxiway Alpha 2 with taxiway Bravo, to be designated as a hot spot. [SR24/2017]
- that the Sharjah Department of Civil Aviation re-assess the risk associated with the visibility of previous runway markings, and the width of taxiway Bravo as part of the Aerodrome Runway Safety program. [SR25/2017]
- that the Sharjah Department of Civil Aviation together with Sharjah Air traffic Services - Serco Middle East address the limitations and associated risk affecting the controller’s performance within the Tower visual control room. [SR26/2017]
- that the Sharjah Department of Civil Aviation re-assess the need of surface movement radar to assist controllers in improving the monitoring of aerodrome movements. [SR27/2017]
- that the Sharjah Department of Civil Aviation ensure that the manuals issued by Sharjah Air Traffic Services contain the correct information to reflect the current GCAA approval for runway 12/30. [SR28/2017]
- that the Sharjah Department of Civil Aviation re-address the process of updating the Aerodrome Manual and ensure that it is revised to reflect the current status of the aerodrome. [SR29/2017]
- that the Sharjah Department of Civil Aviation review the limitations on taxiway Bravo 11 to Alpha 12 and determine whether or not they should be included in the Aerodrome Manual and the UAE AIP and whether this intersection should be declared a 'Hot Spot'. [SR30/2017]
- that the Sharjah Department of Civil Aviation review and ensure that the information on the Jeppesen plates and UAE AIP for Sharjah aerodrome reflects the Aerodrome status. [SR31/2017]
- that the Sharjah Department of Civil Aviation review and implement procedures for the immediate notification of serious incidents and accidents to the AAIS. [SR32/2017]
- that the General Civil Aviation Authority (GCAA) of the United Arab Emirates share this Report (AIFN/0011/2015) with the UAE National Runway Safety Team (NRST) and all Local Runway Safety Teams, emphasising the safety recommendations contained herein. [SR33/2017]
- that the General Civil Aviation Authority (GCAA) of the United Arab Emirates monitor both Sharjah Air Traffic Services and Sharjah Department of Civil Aviation for the implementation of the safety recommendations within this Report, AIFN/0011/2015. [SR34/2017]
The Final Report of the Investigation was issued on 13 April 2017.