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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 person in charge on the flight deck of the aircraft has given their confirmation of ‘brakes released’ to the person in charge of the ground crew vehicle who are to carry out the tow, the ground crew become 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. When any ground locking pins are fitted to an aircraft for towing (or any other purposes) or when they are subsequently removed, it is usual to require the recording of such 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 a ground crew team carrying out an aircraft tow include ensuring that no part of the aircraft structure will impact any fixed object, vehicle, or other aircraft. The ground crew should have intercom communication with the personnel on the flight deck and both parties should be able to listen to communications with ATC. In the absence from the flight deck of a pilot qualified on the aircraft type, The person in charge of the ground vehicle carrying out the tow will usually be responsible for obtaining any necessary ATC aircraft movement clearances.
The function of any flight deck occupant(s) is likely to be 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 where available, an 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 flight safety
The key threat to aircraft flight safety consequent upon towing operations is collision between the aircraft under tow and another aircraft. Two 'types' of collision with potentially high risk outcomes exist:
- a collision with a moving aircraft taking off or landing on an active runway whether or not the aircraft under tow has a valid ATC runway occupancy clearance.
- impact damage to another, usually stationary and unoccupied, aircraft caused by undetected relatively minor impact which is then not detected prior to either damaged aircraft departing on a flight.
Ground Crews must be specifically made aware of both these risks and must be fully trained on both ATC practices and the towing of the particular aircraft type involved. The later should include awareness of aircraft dimensions and turning arcs.
- A failure to maintain overall situational awareness of other traffic regardless of whether a required ATC clearance is held
Inadequate RTF skills on the part of the persons responsible for communicating with ATC from the towing team.
- 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.
- Inadvertent or otherwise inappropriate brake application during towing by personnel ‘riding the brakes’
Towing collision risk is exacerbated by the conduct of such operations during the hours of darkness or in poor ground visibility and procedures should effectively address and/or constrain such operations.
- ICAO Doc 444 PANS-ATM Chapter 22.214.171.124 in respect of RTF phraseology
- ISAGO Standards Manual 5th Edition, March 2016
- Accident and Serious Incidents: Ground Operations:
- AC 150/5210-20A: Ground Vehicle Operations to include Taxiing or Towing an Aircraft on Airports, FAA, September 2015.