Before my latest flight out of LAX last week I was listening to Ground North. Apparently a SW pushed back. ATC asked them if they were ready to go and the response was something along the lines of "It's going to be a little longer because we're a MAX". Maybe I heard it wrong but it was definitely SW and it was definitely ground talking to that a/c.

Is there anything in particular that is unique to the MAX that it would require the crew a few more moments to actually taxi after push back?

Both the LEAP and GTF are slower to start then the previous V2500 or CFM56 series engines. This is not a Boeing/MAX issue as the same situation exists on the neo. It’s part of the trade off of higher tolerances and better thermal performance. The start sequence itself just takes longer, largely due to dry motoring to even out rotor bow from heat soak.

Yes, Genx and Leaps are slower when it comes to engine starts. Maddening how long it takes to start up 747-8s.

The motoring sequence can be as long as 2 or 3 minutes. So in LAX when you get pushed in to the alley, ramp is chomping at the bit to get you moving.
The push crew has disconnected and driven off, but the fadec is still motoring the engine and hasn’t even thought about doing the engine start sequence yet.

Meanwhile everyone is holding on the gate for you to get out of the way and ground is holding inbound aircraft waiting for your engines to finish motoring.

So its always two engine taxi for a NEO, otherwise I’ll be doing the same thing at the end of the runway waiting for the second engine to start plus the 5 minute warm up after engine start before I can apply takeoff power.

Woodreau wrote:

So its always two engine taxi for a NEO, otherwise I’ll be doing the same thing at the end of the runway waiting for the second engine to start plus the 5 minute warm up after engine start before I can apply takeoff power.

Can't you just have the FO start the second engine during taxi?

Ive found that if i dont have the second engine started before i start taxiing, i am going to be waiting at the end of the runway for the warmup timer to reach 5 minutes…. Maybe when airport congestion returns and taxi times increase to more than 10 minutes, then maybe i might consider starting the second engine during taxi.

It already takes around 5 minutes to get a NEO engine started, so it’s a 10 minute process to have an engine ready for takeoff.

On a normal IAE engine, the engine starts within 3 minutes, and i can apply takeoff power 3 minutes after the engine has completed the start procedure. So the 4 minutes extra for a NEO engine impacts things a little bit.

Okcflyer wrote:

Both the LEAP and GTF are slower to start then the previous V2500 or CFM56 series engines. This is not a Boeing/MAX issue as the same situation exists on the neo. It’s part of the trade off of higher tolerances and better thermal performance. The start sequence itself just takes longer, largely due to dry motoring to even out rotor bow from heat soak.

It is the only complaint my friends has when he has flown the MAX, otherwise loves it.

Woodreau wrote:

The motoring sequence can be as long as 2 or 3 minutes. So in LAX when you get pushed in to the alley, ramp is chomping at the bit to get you moving.
The push crew has disconnected and driven off, but the fadec is still motoring the engine and hasn’t even thought about doing the engine start sequence yet.

Meanwhile everyone is holding on the gate for you to get out of the way and ground is holding inbound aircraft waiting for your engines to finish motoring.

So its always two engine taxi for a NEO, otherwise I’ll be doing the same thing at the end of the runway waiting for the second engine to start plus the 5 minute warm up after engine start before I can apply takeoff power.

I don't want to get too off-topic, but if it's the first flight of the day, does the start go quicker because the engine is cold throughout? I've had only one MAX flight and we didn't sit like that, but it was the first of the day.

When you initiate an engine start, the FADEC does it's thing and comes up with a countdown of how long it needs to motor the engine... On the first flight of the day, the FADEC comes up with the answer "Cooling Time 0:00" so there is no motoring of the engine. The engine starts immediately... 3 minutes later the engine is at ground idle. however there is still a 5 minute warmup after engine start. So the time is reduced from 10 minutes to 8 minutes, by not having to motor the engine.

Edit: And to be clear I am describing a PW 1100 NEO engine on an A320, not the 737 MAX engines. So I apologize for derailing this thread off topic of the 737 MAX engines.

Is it possible to "pre-motor" the engines as you prepare for pushback, or does motoring need to be done immediately before the start sequence?

DocLightning wrote:

Is it possible to "pre-motor" the engines as you prepare for pushback, or does motoring need to be done immediately before the start sequence?

In theory you could crank them, but ground crew don't really want spinny spinny stuff spinning until they've cleared you to start engines.

Also, not part of the procedure.

Cranking is not done before the start sequence. It's an automatic thing that forms part of the sequence as needed on the aircraft I fly.

DocLightning wrote:

Is it possible to "pre-motor" the engines as you prepare for pushback, or does motoring need to be done immediately before the start sequence?

Doc, theoretically, it is possible. However, to initiate rotation on the engine(s) while still parked at the gate--prior to pushback--can introduce hazards to the ground crew and is, therefore, not routinely done. The only time we actually start an engine at the gate is in the event the APU is inoperative, using an air cart capable of supplying high pressure air, but this is done using very strict procedures coordinated with the ground crew as well as ground control or ramp control, as appropriate.

With regard to "pre-motor," as you mentioned, on the Airbus A320 series equipped with CFM-56 engines, this is referred to as a "manual" start, but it is only used under certain conditions specified in company operating procedures and it is accomplished using appropriate procedures. To accomplish a manual start in order to reduce engine start time would be a violation of company procedures and is therefore not done (unless the specified conditions exist, of course).

e38

Woodreau wrote:

The motoring sequence can be as long as 2 or 3 minutes. So in LAX when you get pushed in to the alley, ramp is chomping at the bit to get you moving.
The push crew has disconnected and driven off, but the fadec is still motoring the engine and hasn’t even thought about doing the engine start sequence yet.

Meanwhile everyone is holding on the gate for you to get out of the way and ground is holding inbound aircraft waiting for your engines to finish motoring.

So its always two engine taxi for a NEO, otherwise I’ll be doing the same thing at the end of the runway waiting for the second engine to start plus the 5 minute warm up after engine start before I can apply takeoff power.

Yeah, the alley between T1 and T2 can get really cramped if the 764 JFK flight is at the A21and an A350 is at 25A along with all the other flights. T3's completion will help a lot.

Thanks for all the explanations.

On the MAX, it's called "bowed rotor motoring". When the engine is shutdown, dissimilar cooling of the different metals causes the main shaft to bend, or "bow".

When you start the engine, the EEC does some magic, and decides how long the engine needs to motor, to straighten the shaft. A "MOTORING" annunciation is displayed over the N2 gauge until the computed time is up. When the MOTORING goes away, you can introduce the fuel and complete the start.

The longest motoring time I can remember was one minute, forty seconds. So you are potentially looking at around three minutes from initiation of the start, to stabilized idle. Per engine.

My airline has a small fleet of A321neo with LEAP engines. When the engine is cold, start up takes about a minute. When it's warm, you're looking at 1 minute 40 seconds to start and then a 3 minute warm up period before takeoff.

I love our MAX engines. They take soooo long to start in comparison but once they do the sound they produce is lovely. Oh and I get paid more as every minute counts. Controllers seem to be aware the NEO’s and MAX’s just take longer to get going.

Snuffaluffagus wrote:

My airline has a small fleet of A321neo with LEAP engines. When the engine is cold, start up takes about a minute. When it's warm, you're looking at 1 minute 40 seconds to start and then a 3 minute warm up period before takeoff.

Quick question: is that 3 mins before you can advance the throttle, or 3 minutes before you can apply take-off power?

fr8mech wrote:

Snuffaluffagus wrote:

My airline has a small fleet of A321neo with LEAP engines. When the engine is cold, start up takes about a minute. When it's warm, you're looking at 1 minute 40 seconds to start and then a 3 minute warm up period before takeoff.

Quick question: is that 3 mins before you can advance the throttle, or 3 minutes before you can apply take-off power?

Take-off power

It’s something ATC gets used to, the other day I Gad southwest do a long push all the way out of the alley so I could push a delta who called Roth after them into the alley. The thing was, knowing they are a max, I will adjust the plan accordingly.

DocLightning wrote:

Is it possible to "pre-motor" the engines as you prepare for pushback, or does motoring need to be done immediately before the start sequence?

Realistically, no, because it would probably not be safe to spin engines (even at a low speed) until the jetbridge is moved back to a safe parking area, all ground equipment is removed, and a member of the ground crew confirms that the area around the engines is clear and safe. I suppose it would be safe to motor the engines if a crew is ready for pushback but can't actually start the push due to ramp congestion, but I don't believe any aircraft or operator is set up for this procedure.

On a side note, the 320 NEOs with the Pratt engines have an option available to motor (cool) both engines during the start sequence of the first engine. This reduces overall starting time by a minute or two.