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Push and Hold
From SKYbrary Wiki
This is a procedure adopted by some aircraft operators when ATC have advised of an expected significant delay for take off so as to allow their flights to record an on-time departure and / or to clear a gate for re-use. If the airport operator directly controls gate occupation, then the procedure may also be used by them for gate-release purposes. It involves an aircraft ground-positioning, usually under its own power, to what are often specially designated remote parking stands. Here, the engines are shut down and aircraft services are maintained by the use of the APU until engine re-start is authorised by ATC.
Operational Safety Implications
The only issue raised is the absence of ground supervision of the engine restart at the remote parking position. This absence also implies a lack of aircraft fire cover during engine start which is contrary to the case for normal pre-flight engine starts which take place either on the turn round parking gate or during / immediately after the pushback with the ground crew in attendance and in communication and ground fire extinguishers in proximity to the aircraft. Risk Assessment processes usually note that the vicinity of the aircraft in the restart area can safely be assumed to be clear, and identify the overall mitigation for the lack of external observation and a portable ground fire extinguisher as the extremely low probability of any hazardous engine start fire, given the improvements in turbine engine design which have prevailed in recent years. The most likely abnormality during an engine start, a tail pipe fire during the start cycle, is both essentially non-hazardous and produces characteristic indications which are readily evident to the flight crew.
In respect of cold weather operations, at most airports where push and hold occurs, Ground De/anti Icing will take place after engine restart but if is has occurred beforehand, the delay may use up a significant amount of Holdover Time which, dependent upon the availability of repeat de icing, may reduce the operational advantage of push and hold.
Proactive risk management should be based upon Flight crew and ATC awareness of potential safety issues and any procedural mitigations of them. In particular, Operations Manual Procedures should clarify the actual and the potential effect of starting engines without the presence of ground fire cover from a start crew. In certain circumstances, for example the use of particularly remote positions for prolonged holding of departing aircraft with engines shut down, there may be an exceptional case for ground supervision of engine re-starting but in almost all cases, the airport RFFS will be able to reach all parts of the airside area within a relatively short time as dictated by regulatory requirements.
For operational purposes, there should be an ATC and / or Company procedure which provides for early notification of an intention to issue and / or accept a push and hold gate departure clearance, so that any appropriate loading of additional fuel for the running of the APU when holding remotely is facilitated.