The taxying of twin engine aircraft using only one engine or the taxying of aircraft with more than two engines with one or more engines shut down.
Due to the multiple safety, efficiency and operational factors which vary for every aircraft, airport lay-out, weather conditions, surface conditions and traffic load, Engine Out Taxying (EOT) procedure, when permitted by the operator, should not be mandatory and aircraft commanders should always be required to assess whether it is appropriate.
How to Enable EOT as a Safe Procedure
The incorporation of an approved, standardised EOT procedure into the applicable Operations Manual, as part of taxying procedures should always occur if the procedure is to be available. These EOT procedures should mirror manufacturer protocols, where published, and must clearly identify and address any areas of potential confusion such as responsibilities and task allocation during start up and shutdown. They should also provide guidance on when EOT may or may not be used. The procedure should specify whether engine starting may be carried out whilst the aircraft is taxying and if it is, then appropriate and explicit guidance on how this can be safely achieved should be provided. In general, the Operations Manual entry must clearly state that any EOT is carried out entirely at the aircraft commanders discretion after careful consideration of all location-specific and operational circumstances.
Such operational circumstances include but are not necessarily restricted to:
- Local airport conditions which may militate against such operations, for example taxiway/ramp surface gradients
- Proximity of other aircraft, vehicles and personnel when using EOT during taxy-out as break away thrust requirements must be satisfied with fewer engines
- Manoeuvring freedom in respect of turn radius and direction of turn
- The ability to satisfy AFM engine warm-up and cool down times for thermal stabilisation
- During cold weather operations, consideration of the time it will take to reach the minimum oil temperature requirements for application of take off thrust
- The prevailing weather and surface conditions
- The need to accomplish procedures related to aircraft system monitoring and checklist completion despite a delayed engine start (during taxy-out) and/or an early engine shut-down (during taxy-in)
Some Practical Considerations
If the aircraft commander elects to carry out an EOT procedure after considering the above points, the following factors should be taken into account:
- Caution must be exercised when taxying with one (for twin engine) or two engine(s) shut down, to compensate for the possible asymmetric force. This is especially critical when there is surface contamination
- Slow and/or minimum radius turns in the direction of the operating engine may not be possible at high gross weight.
- Aircraft system operation need to be carefully considered to ensure that the critical systems needed for taxying such as Nose Wheel Steering and brake systems remain operative. This may require the activation of electrically driven hydraulic pumps.
- An engine start procedure requires time and attention, which should not be detrimental to other taxying duties, such as external visual scanning, systems monitoring and checklist accomplishment. Consideration should be given to the expected departure route and number-in-sequence relative to the time needed for engine start and “after start” items.
In particular, an engine should not be started:
- By the pilot controlling the aircraft unless it is stopped and the park brake has been applied;
- When taxying on an apron or within a complex taxiway layout;
- When crossing an active runway;
- When taxying in low visibility conditions.