Pushback means the movement of an aircraft from a nose-in parking stand using the power of a specialised ground vehicle attached to or supporting the nose landing gear. It is commonly the second part of a ‘Taxi In Push Out’ (TIPO) procedure at airport terminal gates and will be necessary to depart from all except self manoeuvring parking stands unless the aircraft type is capable of powerback and local procedures allow this. Occasionally, a pushback may need to be followed by an engines-running pull forward to a position where local procedures allow aircraft to move forward under their own power, but usually, ground vehicle disconnection will occur after the completion of a pushback.
Once the aircraft commander (or other person in charge on the flight deck if the aircraft is not in service) has given their confirmation of ‘brakes released’ to the person in charge of the ground crew who are to carry out the pushback, the ground crew become temporarily responsible for the safe manoeuvring of the aircraft in accordance with either promulgated standard procedures or as 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. Usually but not always, this will be obtained by the aircraft commander or other person in charge in the flight deck. The prescribed RTF phraseology for pushback is contained in ICAO PANS-ATM.
Formerly, almost all aircraft types required that the ground locking pin be installed in the nose landing gear during any pushback; however, this is now no longer always the case. If a ground locking pin is installed for the pushback, it will need to be removed after the completion of the ground vehicle manoeuvre if the aircraft has been pushed back prior to intended flight.
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. The same towbar attachment and ground vehicle may also be used for Aircraft Towing in the forward direction. An alternative method which is becoming more common for pushback 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. These specialised vehicles can also be used to tow aircraft forward,
Both pushback methods are subject to the observance of any aircraft limits for maximum nose landing gear steering angle, but these are not usually especially restrictive.
The responsibilities of the ground crew team carrying out a pushback include ensuring that no part of the aircraft structure will impact any fixed object or other aircraft and may include giving clearance to start one or more engines just before, during or immediately after a pushback. The number of people assigned to a ground crew team for a pushback may vary according to aircraft size, but in most cases will be at least three. One will be driving the pushback vehicle, one will be walking in the vicinity of one of the aircraft wingtips and looking beyond the aircraft tail and one will be in charge of the manoeuvre and in communication with the person with aircraft responsibility in the flight deck. Communication between the ground crew supervisor is usually by means of a plug in to an aircraft ground intercom circuit; if so, this is facilitated by a ground crew microphone which acquires the voice of the user whilst excluding background noise, which if the aircraft engines are running can be considerable. If only two ground crew are used for pushback of a smaller aircraft then it is important that the procedure takes full account of the roles of each ground crewmember and that the person in charge of ground crew communications on the flight deck is aware of the number of ground crew being used and the physical location of the supervisor.
Effective communication between the person in charge in the flight deck and the person in charge of the ground crew, and between the members of the ground crew team is critical. If the aircraft is being pushed back prior to intended flight and the person in charge of the flight deck is therefore an aircraft commander, the procedures of the aircraft operator may require that the designated Pilot Flying, who may be the co pilot, should oversee the pushback and in this case all communications with the ground crew will be undertaken by that person rather than necessarily by the aircraft commander. If it is considered that communication by hand signals rather than intercom is acceptable then it is essential that the applicable procedures are comprehensive and thoroughly understood by both parties and that they cover all possible abnormal and emergency circumstances.
The case of engines-running pull forward as a supplementary action prior to ground vehicle disconnection after a pushback should be considered as part of the pushback procedure and trained accordingly since it bears little practical resemblance to the towing for longer distances of empty out-of-service with engines stopped.
Engine Starts may be routinely accomplished immediately before or during pushback. Where they are carried out when the aircraft is moving, it is essential that the ground crew supervisor does not allow the checks and communication required in connection with engine starting to interfere with their primary responsibility to control the pushback and remain in full communication with those on the flight deck using the means available. Many aircraft operators require that when push back is accomplished without headset communications, engine starts do not take place whilst the aircraft is being pushed, preferring instead to require that engine starting takes place before or after completion of the pushback. Observations of abnormal circumstances in connection with engine starts or any other matter affecting, or potentially affecting the safety of the aircraft during a pushback are of great importance to those on the flight deck but it is essential that any descriptions of external observations during engine starts are imparted accurately; this may sometimes be demanding using ground intercom but can be extremely difficult with only hand signals available.
The key threat to aircraft safety
If damage is caused to the aircraft on pushback, or to another aircraft by the aircraft on pushback, this must be identified and technically assessed before that aircraft flies. Unfortunately, this is not always the case. It is important to recognise that when part of one aircraft impacts part of another aircraft, the degree of resultant damage may vary between negligible and major, even if the aircraft are identical. Ground Crews must be effectively briefed on this as well as other aspects of the operation. This is especially important when the ground crew are not employed directly by the aircraft operator or if they do not speak the same language fluently for operational communications.
The evidence of accidents and incidents is that there are a number of recurrent features of aircraft damage during pushback:
- Use of hand signals rather than intercom communication,
- Lack of intercom clarity in communications between the aircraft and the ground crew supervisor,
- Ground crew totalling less than three people,
- Departure from non-airbridge gates,
- Failure of vehicle driver to maintain adequate communication with supervisor,
- Lack of clearance between horizontal stabilisers of adjacent ‘T’ tail aircraft,
- Pushback commenced from a parking position different from that marked,
- Ground crew poorly trained or unfamiliar with the immediate pushback environment,
- Unserviceable towbars attributable to lack of ownership clarity,
- Surface contamination obscuring pavement markings.
Accidents and Incidents
The following events in the SKYbrary database occurred during Pushback:
On 28 March 2018, a Boeing 767-300 and a Boeing 737-700 were being simultaneously pushed back in darkness from adjacent parking positions as cleared when their respective tailplanes collided causing substantial damage. The comprehensive Investigation found that the 737 clearance conflicted with both a previously-issued clearance to the 767 aircraft and with the actual location of the 737. It also found that the controller’s error had been compounded by the wing walkers tasked with external monitoring of both pushbacks being in the drivers’ cabs because it was raining and a context of systemic ramp operations inadequacy was identified as contributory.
On 13 February 2019, a Boeing 787 departing Amsterdam was given a non-standard long pushback by ATC in order to facilitate the use of its stand by an incoming flight and when a Boeing 747 was subsequently given a normal pushback by a single tug driver working alone who was unaware of the abnormal position of the 787 and could not see it before or during his pushback, a collision followed. The Investigation concluded that the relevant airport safety management systems were systemically deficient and noted that this had only been partially rectified in the three years since the accident.
On 16 June 2021, a Boeing 737-400 was taxiing for departure at night after push back from stand when the ground crew who completed the push back arrived back at their base in the tug and realised that the tow bar they had used was not attached to it. The aircraft was prevented from taking off and it was then found that it had taxied over the unseen towbar and sustained damage to both nose gear tyres such that replacement was necessary. The Investigation concluded neither ground crew had checked that the area immediately ahead of the aircraft was clear.
On 23 March 2019, the crew of a fully-loaded Airbus A320 about to depart Bristol detected an abnormal noise from the nose landing gear as a towbarless tug was being attached. Inspection found that the aircraft nose gear had been impact-damaged rendering the aircraft no longer airworthy and the passengers were disembarked. The Investigation noted that tug driver training had been in progress and that the tug had not been correctly aligned with the nose wheels, possibly due to a momentary lapse in concentration causing the tug being aligned with the nose leg rather than the nose wheels.
On 30 March 2017, a Boeing 787 taxiing for departure at night at Singapore was involved in a minor collision with a stationary Airbus A380 which had just been pushed back from its gate and was also due to depart. The Investigation found that the conflict occurred because of poor GND controlling by a supervised trainee and had occurred because the 787 crew had exercised insufficient prudence when faced with a potential conflict with the A380. Safety Recommendations made were predominantly related to ATC procedures where it was considered that there was room for improvement in risk management.
- ICAO Doc 444 PANS-ATM Chapter 126.96.36.199