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The forward movement of an aircraft, usually with engines off, using the power of a specialised ground vehicle attached to or supporting the nose landing gear. It may occur for the movement of both in service and out of service aircraft. This will affect the promulgation of procedures and the required qualification for those occupying the flight crew seats on the aircraft during the manoeuvre. As part of out of service repositioning of aircraft supervised by maintenance personnel, it may follow the Pushback from a nose-in gate of an empty aircraft with engines off.
Once the aircraft commander (or other person in charge on the flight deck if the aircraft) has given their confirmation of ‘brakes released’ to the person in charge of the ground crew who are to carry out the tow, the ground crew become temporarily responsible for the safe manoeuvring of the aircraft in accordance with any ATC clearance which may be required and as may have been specifically agreed beforehand.
Unless the manoeuvre is taking place outside the movement area controlled by ATC, an RTF clearance to carry it out will be required. If the aircraft is being towed to a start position or to a Push and Hold location, this normally will be obtained by the aircraft commander or other person on the flight deck. If an out of service aircraft is being repositioned, the clearance will normally be obtained by the operator of the tow vehicle. The prescribed RTF phraseology for obtaining clearance to tow is contained in ICAO PANS-ATM.
Formerly, almost all aircraft types required that the ground locking pin be installed in at least the nose landing gear during any towing operation but this is no longer always the case. If a gear ground lock pin is installed for the tow, it may need to be removed after the completion of the manoeuvre. If any ground locking pins are fitted to an aircraft for towing purposes, it is normal to record the action in the Aircraft Technical Log
The ‘traditional’ method of allowing the ground vehicle to move an aircraft is to attach it to the aircraft nose landing gear by means of a towbar. These must be approved for use with a particular aircraft type and clearly marked as such since there is no universal towbar specification. An alternative method which is becoming more common for towing is the use of a specialised vehicle called a ‘towbarless tug’. This positions two low level ‘arms’ either side of the aircraft nose landing gear and these are used to engage with the aircraft gear leg and raise it slightly off the ground.
All towing is subject to the observance of any AFM limits for maximum nose landing gear steering angle.
The responsibilities of the ground crew team carrying out a tow include ensuring that no part of the aircraft structure will impact any fixed object, vehicle, or other aircraft. The ground crew must have intercom communication with the people occupying the flight crew seats and both parties should be able to listen to ATC communications. The ground vehicle carrying out the tow will usually be responsible for obtaining necessary ATC aircraft movement clearances.
The function of the flight deck occupants is likely to be only the appropriate operation of the aircraft braking system and the provision of sufficient aircraft electrical power to operate the radio and appropriate external and internal lighting. It is likely that in most cases, the APU will be running to provide electrical power and that hydraulic accumulator pressure for braking will be achieved by use of an electrical pump.
The key threat to aircraft safety
The key safety threat is damage caused to another aircraft by the aircraft being towed, of which there is no awareness at the time and which is then not detected prior to the damaged aircraft departing on a flight. Ground Crews must be effectively briefed on this risk and must be fully trained on the towing of the particular aircraft type with special reference to its dimensions and turning arcs.
- Inadequate awareness of aircraft dimensions and turning arcs by the ground crew towing
- Lack of clearance between horizontal stabilisers of a towed ‘T’ tail aircraft when it is turning in proximity to another similar ‘T’ tail type.
- Failure to keep towed aircraft on the taxiway centreline or other taxi guidance line.
- Inadequate RTF skills on the part of the persons responsible for communicating with ATC from the towing team.
- Inadvertent brake application during towing by personnel ‘riding the brakes’