Originally Posted by
Tu.114
Me, I am unconvinced of this procedure. Having the PM heads-down during taxi is not a good idea. Requiring a not insignificant thrust setting that will have to be kept against all instincts when the aircraft is speeding up comes with the above described consequences, inadvertently idling the engine may do interesting things to the start cycle that will not save much time. Also, how do You time the startup? The engines require warmup times from 2 to 5 minutes - starting the engine too late may well have You wait at some holding point until that time has elapsed while the precious juice runs into both engines. There will certainly be a rise in takeoffs with improperly warmed up engines, at least in the beginning, as well.
Adding up to the great posts above about SETWA (Single Engine Taxi Without APU), a couple of things about what you said:
- PM heads down during taxi: The procedure states that the application of the procedure is at pilot's discretion if the crew considers the workload will increase significantly (unduly)
- As mentioned, the increase in thrust is not massive. The thing already idles at about 20% N1 and in a CEO you will get good start pressure at around 30%. While a NEO will increase thrust by itself, since it detects the X bleed start condition.
- If you had a green arc on a brake, you should have put the brake fans on when starting to taxi. Which means that by the start of the second engine, you already gained some brake temp margin.
- I've had a couple of FOs idling a starting engine. If you catch it soon enough, you can set the thrust back and you will get a normal start. Otherwise you'll get an ECAM for low start pressure and the FADEC will take care of it. I haven't really heard of anyone botching an engine because of an erroneously idling donor engine.
- You will get the timing right as you get familiar with the procedure, and based on your knowledge of the traffic flow of any particular airport. Begin with a bit of extra time on your side as you get the hang of it and you learn how to judge it, as we do with any new procedure
- Depending on the operating culture of your company, you may or may not get improperly warmed up engines at takeoff. I've flown for two South American operators with this procedure in place; one of them has been doing this for some years now, the other one about a year ago. The former seemed to have no such occurrence, or very few; the latter seemed to have a bit more of such cases. Care to take a guess at which operator seemed to have a better discipline culture?
Resistance to change is in all of us as humans, so I get your point. But many operators around the world have been doing this for quite some time now, and continue to do so. If it wasn't beneficial somehow, they've had stopped doing this or have some concerns or even more restrictive conditions to perform SETWA. Airbus is quite specific regarding the conditions in which it is or is not acceptable to apply this procedure (including MEL items), and companies tend to make it even more specific.