How Single-Engine Taxiing Works and When is it Used?

When thinking about the take-off procedures of a multi-engine aircraft, one would assume it requires all its engines while taxiing. That is the perception among the public, but it is interesting to note that there are instances where taxiing is completed using a single engine. 

The single-engine taxiing approach is cost-effective, and its environmental impact is somewhat less than the multiple-engine taxiing. There are certain situations which demand single-engine taxiing. 

Let us look at how single-engine taxiing works and when it is used.  

Probability of Single-Engine Taxiing 

Most airlines instruct their pilots to use only a single engine for taxiing if it is possible in the circumstances, the main factor while considering this is whether the force or thrust generated by a single engine would be enough to taxi the plane safely. 

If the load on the aircraft is too much, then the possibility of single-engine taxiing is less. A heavily loaded aircraft will require more thrust than a single engine could produce to move away from a standstill. Pilots can guess if a single-engine approach would work based on the ramp weight and rely on their experience for judgment. 

Scenarios Not Suitable for Single-Engine Taxiing 

Taxiways which are tightly packed with buildings or equipment, like near terminals or gates, require aircraft pilots to be extra careful that they do not knock off things like cargo carts, jet bridges or any other vehicles with their thrust. Using two engines instead of one for taxiing will reduce the power needed to break away from standstill and significantly reduce the chances of causing damage. 

Having multiple engines turned on while taxiing can assist in smooth turning at sharp corners, they can increase the power on the engine that is outside of the turn for easier steering. 

Another thing pilots consider when using the single-engine taxiing method is the length of the taxiway. Engines require a cool down time of roughly about 2 to 4 minutes before being completely shut off. If the taxiway is quite short, the engine may not get this time before it reaches the end to be parked. The engines must be shut off as soon as possible after parking to ensure the safety of the workers on the ramp. Although the ramp crew are aware not to approach until the red signal is turned off, which indicates that the engine is shut off. 

Single-Engine Taxiing at Busy Airports 

At busy airports like Heathrow, New York and Dallas, single-engine taxiing is immensely helpful. At these busy airports, take-off usually requires about half an hour, so pilots can use the single engine to taxi for the first 20 minutes and then start their other engines when they are closer in the line to take off. This can help them use the minimum amount of fuel for take-off and can be cost-effective. 

Contamination on the Taxiway 

If there is still water, ice, snow or slush on the taxiway, pilots are not allowed to use single-engine taxiing, as using multiple engines makes the aircraft easier to manoeuvre and can help reduce chances of any accident on the runway. 

You as a passenger can also notice this if you notice only one engine coming to life during take-off, or one engine shutting down during landing. Single-engine taxiing is very useful when it is operationally feasible under the right conditions.