A320 OETD w/ Crossbleed Start
 

Hello All
My mob has recently modified standard SOP to include the use of single-engine-taxi departure but with switching the APU off after the first engine start in the name of fuel-saving. The crew then start the second engine using the established cross-bleed start procedure. In some of the peripheral documentation around it's introduction, it was mentioned that many other airlines (I seem to recall North American ones specifically) have already adopted this, and that it happens all the time. True? Thoughts?
FFR

Here, we do not do such a thing. A crossbleed is done while standing, usually after the push, and always with ATC approval due to higher than normal jet blast.

A crossbleed on a CEO requires 25 and prefers 30psi of bleed pressure. This will cause a noticeable amount of thrust as a byproduct that is sometimes needed and sometimes unwanted during taxi. Pulling the donor engine back to idle during a crossbleed is not advisable and has to be consciously avoided during such a start. What happens to the unwanted surplus energy, then? It has to go into the brakes.

I trust that Your company has considered the increased wear on the brakes and also the possibility of high brake temperatures after takeoff (after all, the temperature takes a while to peak after an application). Are You required to taxi with the brake fan on even without the green arc showing when applying this procedure?

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.

This procedure may well just shift costs from fuel over to maintenance. But I trust that the company has done its math before implementing such a SOP change.

TBF, on a PW NEO engine, the thrust lever can remain at idle during the crossbleed engine start, so there will be no “temptation” of reducing trust, as you won’t be able to, and on a CEO you can’t do SET without the APU running due to the engine fire suppression system not working correctly in case of emergency electrical configuration on the ground. And usually the company will have more information than the pilots on how much things cost, so if they’ve implemented a procedure, it is probably worthwhile.

For the CEO it depends. If the CEO is retrofitted for single engine taxi without APU it can do the 2nd engine start without APU as well. The orange bunch has done it on nearly if not all of their CEOs for example. Saves some fuel on taxi in.

Yeah, that’s the old procedure. We know that. Now we can choose how we cross bleed start, either during taxi or the old fashioned way ;)

Yes, you need a bit of thrust on the live engine during the second engine start, around 28-30% N1 on the live engine. On the CFM NEO it’s even less, around 26%. It’s not an issue really, comparable to the additional thrust you get when you taxi with engine anti-ice on on the CEO. If you can handle that, you can handle the crossbleed!

My home base has a significant downhill taxiway. Like you I was a bit skeptical about this new OETD without APU procedure, but even downhill it works out fine!

As I understand it, it is an Airbus thing. The increase in brake temp is nihil. I have yet to use brake fans as a result of this new procedure.

You get used to the procedure quite quickly. The first couple of times I suggest you only do it during a low workload day as you will have to get used to the procedure. But after a couple of starts it will be second nature. You flick the switches from memory, our colleague set’s the usual thrust, you check the pressure and you start the engine. It’s a non issue.

I have had a colleague close the thrust lever prematurely once, it did not affect the EGT as far as I could see, the start did not fail, he just restored the thrust after I prompted him and the engine started as normal.
It’s their toy. They’ve done the maths together with Airbus. When we started doing OETD with APU 15 years ago, people were just as skeptical: the nose gear would scrub off, fuel flow would be high, engines would catch fire, ATC would go berserk… now it’s normal ops.

I like this new procedure. Yes you will have to get the hang of it, but after that, it’s not much different from a ‘normal’ one engine taxi departure. Why have another jet engine blasting away at 99-100% N1 when you don’t need to?

It’s been a while since last post on this discussion. After a few months (and if more operators have introduced it) what are your thoughts?
I tend to agree with PENKO, I was quite skeptical initially, especially for brake use, but I see it is quite efficient and easy to do. And regarding brakes no big issues. Again at the beginning I used to reduce to below 10 kts before setting N1~30% now I just use one brake application if approaching 30kts….

There‘s plenty of places with uphill taxiways that require thrust anyway. Regarding the head-down, it’s not like starting some old-fashioned mechanical fuel control engine that requires constant monitoring. If you told the PM to just initiate the start and then ignore the engine you’d still save money as start faults are so rare that even the occasional killed engine would not tilt the equation ;-)

Any hints as to which operator the op refers to? Would be interested to learn if/what restrictions are in place and if it’s PWG or LEAP.

In the US is done quite many times, especially at places where taxi times are long. Since you are in a taxiway, there is no harm on increasing thrust above idle as there won't be ground staff or vehicles behind. Be take a look into the plane in front of us and keep a distance, since the note that says that if brakes are applied a small jerk can be noticed. We also avoid doing it in turns to respect the note that nosewheel steering can be lost momentarily, and that coupled with high thrust in one engine could take us into the grass.
I agree that after doing it a couple of times, it becomes kind of memory item, but Airbus provides with a checklist and this is not a flow nor memory item so I would not do it without one in hand. It is quite easy to forget an item in a rush, like for example, forgetting to turn off the electrical Y pump and leave it running all the time.

We are given the option to do the procedure from memory or to use an aide memoire. Most if not all of my colleagues do it from memory just like with the ‘old’ procedure. Actually I now have to stop and think when for whatever reason we are using the APU to start the second engine since, I’m not so used to that flow anymore!

I’m not too worried about forgetting the Y electrical pump. If anything, it tends to inadvertently switch off once the APU shuts down on certain airframes (due to the electrical power transfer), which is the only real issue I have noticed with this new procedure.

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.

We're getting low balled on another !!!!ty pay offer, so I couldn't be bothered with this rubbish. 2 will be started every time and I won't be stressing myself with all this nonsense.