Incident Details
On 12 February 2016, an ATR-72 was towed from parking position 712 via taxiway B1 and its extension to the operator's hangar at Warsaw Chopin Airport (EPWA). Two mechanics qualified for that aircraft type participated in the operation. The tug driver held authorization for towing aircraft and moving on the maneuvering area.
During a right turn towards the EADS gate, the left wingtip struck a lamp post standing opposite the gate. The towing path extension of taxiway B1 is not formally a taxiway and aircraft movement is restricted to towing only. Obstacles including the lamp post and other airport infrastructure are located close to the edge of the path at its final segment near the EADS gate.
Damage
The collision damaged the aircraft's navigation light cover, a lightning arrester on the aileron, and paint on the aileron counterweight. The lamp mast was also damaged.
Contributing Factors
The distance between obstacles and the path allowed towing of an ATR-72 with minimal clearance, requiring great caution. The road geometry at the EADS gate necessitated a very tight turn, increasing difficulty in maneuvering the towed aircraft and raising the possibility of unintentionally leaving the paved area. On the inside of the turn, near the paved edge, there was a deep, muddy puddle with ruts, caused by an earlier careless towing operation by another ground handler the previous day.
The tug driver, concerned that the main landing gear might sink into the ruts on the grass and cause gear damage, focused on precisely avoiding the inner side of the turn. Based on extensive experience, he believed that the wingtip clearance from the lamp post was sufficient. The tug's position relative to the fuselage during the turn hindered observation of the opposite wingtip. A contributing factor was that towing occurred into the sun, which at that time of day was low on the horizon, blinding the tug driver and assisting mechanic.
Preventive Measures
The operator implemented several preventive measures: towing between the hangar gate and taxiway B1 will now include a "wingman" to externally monitor aircraft movement; communication among all participants (tug driver, wingman, observers) must be ensured; actions will be taken to remove or relocate the lamp post; technical personnel will be briefed on the circumstances; and training on "Ground Operations Safety" will be organized.
Probable Cause
The incident resulted from failure to exercise due care by the tug driver and the assisting mechanic in the aircraft cabin.