Airbus Drivers: Single-Engine Taxi 'n APUs

typhoonpilot said:
I ride on Delta a lot and just shake my head when they use significantly more than idle thrust to taxi out on one engine. One engine at high thrust versus two engines at idle thrust, which airplane is burning more fuel? Then the crew are distracted on an active taxiway, often right before takeoff, starting the other engine and finishing up checklists.

I can see doing this in situations where there will be an extended taxi out time, but they are doing it at SLC when there is no traffic and less than 10 minute taxi outs.

In regards to the APU on an A320 can't help you, but remember the DC-9 that crashed into a parked aircraft at Minny a few years back? It's been quite a few years and my recollection is not perfect but old DC-9s had a two position selector for the hydraulic brakes (Left or Right). If you had it in Left and shut down the left engine guess what happened to your brakes when the accumulator ran out of pressure? Newer DC-9s had a Left, Both, Right selector. It was normally kept in the Both position, but a non-normal could have one select either left or right. I forget, or never read, the final report from that incident but upon first hearing about it my thoughts went straight to what position that selector was in and if they had shut an engine down on taxi-in.



Typhoonpilot
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The only DC-9 series that had only a L & R on the brakes was the -10. Anything newer than that, you would have L, Both, R. Regardless of what engine you shut down, with the ALT pump on, you would still have had some pressure going to the left brakes, even with the left engine shut down.
 
B767 said:
Go out on one quite a bit in LA any time we get 24L. Ain't no thing but a chicken wing on a string.

Your whip must be underpowered if even the slum sled can manage it...

;)
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I have that thought on multiple occasions, just not usually on the ground.
 
typhoonpilot said:
I ride on Delta a lot and just shake my head when they use significantly more than idle thrust to taxi out on one engine. One engine at high thrust versus two engines at idle thrust, which airplane is burning more fuel? Then the crew are distracted on an active taxiway, often right before takeoff, starting the other engine and finishing up checklists.

I can see doing this in situations where there will be an extended taxi out time, but they are doing it at SLC when there is no traffic and less than 10 minute taxi outs.

In regards to the APU on an A320 can't help you, but remember the DC-9 that crashed into a parked aircraft at Minny a few years back? It's been quite a few years and my recollection is not perfect but old DC-9s had a two position selector for the hydraulic brakes (Left or Right). If you had it in Left and shut down the left engine guess what happened to your brakes when the accumulator ran out of pressure? Newer DC-9s had a Left, Both, Right selector. It was normally kept in the Both position, but a non-normal could have one select either left or right. I forget, or never read, the final report from that incident but upon first hearing about it my thoughts went straight to what position that selector was in and if they had shut an engine down on taxi-in.



Typhoonpilot
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The fuel burn data suggests otherwise. It's so simple to do the rolling crossbleed (up until this discovery about the fire bottles) there was no systemic reason to not do it. It saves gas, saves engine wear, and so on. It's not much of a distraction... thrust lever a half knob width up, yellow pump off, ignition selector to start, and master switch on.

We only single engine taxi on the left engine due to the hydraulic configuration of the 320 series.
 
Requires more coordination and heads down. Also has to be done when moving (for example waiting in line for takeoff). I'm glad it's not our procedure.
 
Kingairer said:
Requires more coordination and heads down. Also has to be done when moving (for example waiting in line for takeoff). I'm glad it's not our procedure.
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You're going to have to explain yourself a bit better than this? It's a half knob of movement on the thrust lever to get the duct pressure up. It can be done both moving and not moving...
 
PeanuckleCRJ said:
The fuel burn data suggests otherwise. It's so simple to do the rolling crossbleed (up until this discovery about the fire bottles) there was no systemic reason to not do it. It saves gas, saves engine wear, and so on. It's not much of a distraction... thrust lever a half knob width up, yellow pump off, ignition selector to start, and master switch on.

We only single engine taxi on the left engine due to the hydraulic configuration of the 320 series.
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A random bit of information, the engine anti ice generally gives enough bleed to start the other engine with the lever at idle. No it's not our technique and no I don't do it.
 
PeanuckleCRJ said:
You're going to have to explain yourself a bit better than this? It's a half knob of movement on the thrust lever to get the duct pressure up. It can be done both moving and not moving...
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of course it can be done moving and not moving but if your trying to save fuel I don't see the point of using additional power. If youre doing it while your taxiing out with existing thrust, maybe, but I don't get it. Y'all don't have IAEs do you, they don't start quickly.
 
Kingairer said:
of course it can be done moving and not moving but if your trying to save fuel I don't see the point of using additional power. If youre doing it while your taxiing out with existing thrust, maybe, but I don't get it. Y'all don't have IAEs do you, they don't start quickly.
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All GEs here, including the upcoming 321s.

Pratts don't start quickly either though, and the crossbleed is the routine on the 757 fleet, too.
 
PeanuckleCRJ said:
The power required for a crossbleed is less than two engine break away thrust. It's widely accepted around widget land.
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At my last shop we had to set the brake to do a crossbleed start. I'm reasonably sure the same is true here, as I've never done one on the roll.
 
Kingairer said:
My opinion is it's unnecessary and adds workload to an already busy time.
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Kingairer said:
Requires more coordination and heads down. Also has to be done when moving (for example waiting in line for takeoff). I'm glad it's not our procedure.
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.

That was the exact argument that some Northies had when they adopted Southie procedures. From what I observed, didn't take too long for them to change their minds. The only plane in the fleet that crossbleed starts is not a good idea is the MD88. Due to the amount of air required from a low bypass turbojet, the engine has to be almost to takeoff power. That one, we use the APU for a rolling start.
 
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