The non-availability of any advice to the pilots by the airport operator’s dispatch section with regard to restrictions on taxiing and poor lighting have been found to be the cause of a ground collision of two aircraft at Mumbai airport in 2016.
An official probe by the Aircraft Accident Investigation Board into a ground collision between a Kuwait Airways flight which had just landed in Mumbai and an IndiGo aircraft headed for Jaipur has also recommended that the Mumbai International Airport Ltd and the Airports Authority of India treat the incident site as a ‘hot spot’ till a permanent solution is reached. The incident, reported on November 30, 2016, occurred when the IndiGo aircraft was cleared to taxi via a specified path and hold when it reached a particular point.
However, in a few minutes the Indigo flight crew felt the aircraft shaking. The probe report said that immediately after that, they received a call from the Lead Cabin Attendant that a passenger had reported seeing the left wing coming in contact with another aircraft. Kuwait Airways also reported that, “We felt shaky when the Indigo aircraft passed behind.”
The AAIB probe revealed that tghe Kuwait Airways aircraft, an Airbus 330 had swept wings which are subject to a phenomenon known as ‘swept wing growth’ or ‘wing creep’ that occurs during a turn when the wingtip describes an arc greater than the normal wingspan due to the geometry of the aircraft and the arrangement of the landing gear. Though in the present case, the Kuwait Airways aircraft was stationary it had hit its wing.
Damage suffered
The Indigo aircraft suffered damage to the upper section of left hand Sharklet - a vertical wing-tip extension that improves the efficiency of an aircraft - was found sheared off from the main wing structure. The leading edge stainless steel cap of the Sharklet was found damaged from the top edge. Both outer and inner skin of the sharklet was also damaged.
The Kuwait Airways aircraft suffered outboard aileron - panels near the tip of the wing that move up and down - lower skin damage. The out board aileron trailing edge wedge structure was also damaged along with superficial paint scratches to the lower wing surface and wing trailing edge fairings.
Probable cause
The AAIB report said that an assumption by the Indigo flight crew that they were clear of the Kuwait Airways flight had continued taxiing onto taxiway N, thereafter crossing runway 14 without realising that left winglet had contacted the second aircraft.
Safety recommendations
AAIB said that Indigo Airlines may provide guidance material to its flight crew regarding the difficulty associated with assessing wing tip clearance. “MIAL and AAI may review the procedure for taxiing on taxiway N when an aircraft is holding on taxiway W4, short of Runway 14. MIAL may carry out assessment of the visibility conditions in the portion of W4 / N and take necessary corrective action if required,” the report said.