Airliners.net

Hey everyone,

I work for Skywest Airlines as a ramp agent in Denver and subsequently work a lot with mainline United when transferring bags and such to their flights. One thing I noticed about both airlines and never quite understood is that when they pull into the gate, they always leave one engine running until ground power is hooked up. Do most airlines do this? Wouldn't it be cheaper, more fuel efficient, and less costly to just start up the APU on taxi in and shut both engines down when the airplane parks at the gate. Then when ground power is finally hooked up you can shut the APU down. Most of the Skywest planes even have their APU on when they pull into the gate so I don't understand why they keep an engine running. Sometimes a United plane will sit for 5 minutes with the engine running as well while they wait for the jetbridge to be pulled up and only then can they pull out the cable and hook up power.

It just seems to me to be a huge waste of fuel. Or am I missing something technical that I wouldn't know about because I'm not a pilot?

Thanks.

It could be that the APU is unservicable which means they have to leave an engine running until ground power is available.
At AC, pilots usually start the APU on taxi and sometimes shut one engine down, then when they have parked at the gate, they will shut the other one down.
Running the APU is cheaper than running an engine in terms of fuel burn, however, the more the crew starts the APU, then there is more wear and tear on it which leads to higher maintenance costs. It may be just a cheap in the long run to keep an engine running for a few minutes than to start the APU, especially during a short turn where it would have to be started again prior to pushback.

That sounds a bit odd however I'm sure the department the mandates such procedures has thoroughly crunched the numbers on efficiency, wear and tear etc.

Quoting Hatbutton (Thread starter):

I have one question for you, why does it take 5 min. for the gate agent to move the gate. When I was working at SFO I would watch the F9 agents and it took less then a min. to move the gate.

This debate rages every time fuel jumps up a bit. I contend it's best to start the APU so you can shut down the engines immediately upon arrival at the gate. Then, you shut the APU down after ground power is connected--when the rampers have a chance.

Now, I'm sure the suits in Flight Ops. (you know, the guys who run the airline but retire with 2,000 hours total time...) will tell you that, on their orders, the ramp guys are to plug in the power immediately upon arrival. They'll also tell you the ground power rarely fails but when it does, it's NOTAM'ed out. Riiiight...

I know, just shut up and fly the airplane.   TC

Quoting AC_B777 (Reply 1): It could be that the APU is unservicable which means they have to leave an engine running until ground power is available.

No, this, for whatever reason, is UA SOP. Every UA plane that I've ever brought on the gate here in YYZ has run it's #1 engine until the GPU has been hooked up, at which point it shuts down. Why they don't shut down the engines and run off the APU, I have no idea.

Quoting MattRB (Reply 5): No, this, for whatever reason, is UA SOP. Every UA plane that I've ever brought on the gate here in YYZ has run it's #1 engine until the GPU has been hooked up, at which point it shuts down. Why they don't shut down the engines and run off the APU, I have no idea.

That just seems plain stupid. Not only does it burn fuel more fuel....but what ramp agent in their right mind is going to drive a belt loader up to the aft bin and get in with that engine running just above their head. So the ramp crew can't get started on their work until it's off. And if they leave #2 running, then most fuel truck drivers will not even park next to the aircraft until it's shutdown. So not only is it more fuel efficient, it's a safety hazard and causes ramp delays (if you follow the procedures I mentioned). The only pro to this situation is that you cut down on APU maintenance costs. In the overall scheme, that just doesn't seem to justify it to me.

Quoting Devildog2222 (Reply 3):

It doesn't always take them 5 minutes to move the jetbridge up but in certain circumstances it does. At Skywest it's not uncommon for the gate agent to not know the plane has pulled to the gate if their radio isn't working and they are occupied doing something on the computer. At United whenever I stop so as to not drive behind the jet blast, especially early in the morning, the jet bridge had been moved way back into its night parking position. When a 737 pulls up, the jetbridge is really quite far from the airplane and takes a while to position it all the way out and up to the door. And then if the ramper momentarily was occupied doing something else they then come back and finally lower the ground power cable and hook it up. So sometimes yes, it can take a few minutes. And sometimes if everyone's on the ball it will take less than a minute.

Quoting Pilotboi (Reply 6):

At Skywest, they always shut down the number one engine on taxi in. The cargo door on the CRJ 200/700 is right below the engine #1 so with it off we can start downloading the plane without danger above our head. At United I notice they do the opposite engine since the cargo doors are on the other side of the plane so they are not in any danger if one engine is still running. But yes you are right, a lot of the time on quick turns the fueler is there waiting and cannot drive up to the plane and hook up until both engines are off. There may be an APU maintenance cost issue but I'd like to know if that is really true because there is no doubt those 2 minutes of burning fuel each time adds up considering these jets fly 5-6 segments per day.

But then sometimes I'll notice Skywest and United Pilots who do immediately shut down the last engine right when they are chocked in. So I don't know for sure who does and who doesn't do it and what airlines have this policy.

Where I fly, we keep the engines running until the GPU is attached and turned on. We do this because starting an APU would take just as long as waiting for the GPU to be attached. Often, we don't know if we have ground power until we pull up to the gate anyways, so we don't guess and start it up once we are parked at the gate if its needed.

I don't have any numbers, but from my pilot point of view, starting the APU and running it for a couple of minutes while a gate is put in place just doesn't seem to warrant the wear and tear.

Also, I doubt there are any procedures that even refer to this situation. I'd attribute the "running engine" to the fact that most pilots won't start the APU unless they are in the thought process that it is needed. Since the gate is being moved into place, it isn't, so we wait.

At the airlines where they might actually care about this and where this might be investigated as a cost cutting measure, gate positioning is rarely a major issue since they all mostly have one or two fleet types. Furthermore, at these operations, the GPU's are often independent of the jet bridge and can be connected very quickly.

From my arm chair CEO point of view, the way to save money here is in gate staffing and training not in starting an APU to save some fuel.

Checko

Hey

When our pilots arrive at the stand (ramp) the engines are shut down almost straight away… Some Captains even shut them down while the aircraft is still moving (it must only be feet away from the stop point).

When I have been in the flight deck after landing I have noticed the APU being switched on almost straight away after exiting the runway.

Surely leaving the engine/s running increases the danger to ground staff? And also increases the noise for the local residents (something we are more aware of in the UK)

Kimberly.

I believe the estimated cost every time you push the APU Start button on the CRJ-200 is $17 (fuel for start plus wear and tear). Therefore it doesn't make a lot of sense to start the APU for the minute or so that we are usually waiting for ground power to be established.

Quoting Pilotboi (Reply 6): but what ramp agent in their right mind is going to drive a belt loader up to the aft bin and get in with that engine running just above their head

Well, as far as I know, no person is supposed to approach an a/c while the anti-collision lights are on other than to perhaps chock the nose gear and to plug in the ground power.

Quoting Alias1024 (Reply 10): I believe the estimated cost every time you push the APU Start button on the CRJ-200 is $17 (fuel for start plus wear and tear). Therefore it doesn't make a lot of sense to start the APU for the minute or so that we are usually waiting for ground power to be established.

Exactly. If you are running an engine for 20 minutes or more, then it's better to run just the APU if you can, but if you are sitting for a couple of minutes at the gate, then in the long run I think starting an APU is going to cost more, especially during quick turns where the APU would have to be started twice in 30-40 minutes.
I am qualified in APU starts and brake riding on some of AC's planes, and there have been a few times where I have had hung starts and fire warnings and have had to call maintenance to check over the APU. If you have to start an APU just because you are sitting at the gate for 5 minutes, then you risk those things, especially with fire. I believe the cost of an A320 APU is roughly $1.2million, so if you destroy one, then it's going to be a lot more costly than running an engine for a few minutes.

I guess when it all comes down to it, it's up to the pilots what they want to do. If the pilot wants to start the APU or keep the engines running then they will do what they think is best.

Quoting AC_B777 (Reply 11): Well, as far as I know, no person is supposed to approach an a/c while the anti-collision lights are on

Actually, what you are referring to is the beacon. The anti-collision lights (on most aircraft) are the white strobes on the wing tips. These lights are used in the air to attract the attention of other aircraft, hence being called anti-collision. The beacons are the red flashing lights on the top and bottom on the fuselage. When these lights are on, that means one or more engines are running, or the aircraft is getting ready to pushback from the gate.

Quoting Kimberlyrj (Reply 9): Some Captains even shut them down while the aircraft is still moving (it must only be feet away from the stop point).

They may shut one engine down during taxi in, but I doubt they would shut all down until the aircraft comes to a complete stop. You never know if you'll have to stop a few feet short for something, and then continue taxiing which would require some thrust to get moving again.

Quoting TheGreatChecko (Reply 8): I'd attribute the "running engine" to the fact that most pilots won't start the APU unless they are in the thought process that it is needed. Since the gate is being moved into place, it isn't, so we wait.

But pilots also need to be in the thought process that having an engine running at the gate is not the best thing to do. No ground movement can take place, no fuel, no unloading, etc. So next time your flying, consider other things that you may not be able to see in the cockpit. I'm not saying that one way is better then the other, and of course each situation has it's own circumstances, but just remember theres more then just you and your captain working on that flight.

Quoting Pilotboi (Reply 12): Actually, what you are referring to is the beacon. The anti-collision lights (on most aircraft) are the white strobes on the wing tips. These lights are used in the air to attract the attention of other aircraft, hence being called anti-collision. The beacons are the red flashing lights on the top and bottom on the fuselage. When these lights are on, that means one or more engines are running, or the aircraft is getting ready to pushback from the gate

Well, I'm not too sure on what terms are used elsewhere, but at AC, the beacon is also called the anti-collision light and the strobe is called the strobe. The anti-collision light not only applies to other a/c, but also ground equipment and personell.
On Airbus and Boeing a/c that I have worked on, the strobe switch is titled just that, not anti-collision. I have seen the beacon switch also titled anti-collision, so I would think the flashing red light is the anti-collision not the white strobe.

Quoting Pilotboi (Reply 12): But pilots also need to be in the thought process that having an engine running at the gate is not the best thing to do. No ground movement can take place, no fuel, no unloading, etc.

We are aware of this. All we want is for the chocks to be put in then ground power connected. Once those two things are done, we will typically be very happy to shut down the engine(s). This doesn't take very long. Today in PDX, I saw a ground crew establish ground power within 20 seconds of the parking brake being set.

Quoting MattRB (Reply 5): Why they don't shut down the engines and run off the APU, I have no idea.

To save money. AA once published the break-even point for its pilots, but that was some time ago. The only one I accurately remember was 8 minutes for the MD80. Expect longer than 8 minutes from exiting the runway to parking at the gate w/external power applied, then start the APU. Anything less, it was cheaper to keep the engine(s) running and NOT use the APU.

Of course it's cheaper to run the APU than an engine, but it's much cheaper to have ground power and A/C than run the APU. You also have to consider the issue of APU cycles. Those starter generators are busy and they have a finite life. We are encouraged to only fire up the APU about 5 minutes from engine start if we have ground power available and don't need to keep the cabin cool/warm.

The APU on the jets I've flown (ERJ 145 and 170) burn roughly 10 gallons per hour. GPUs are roughly half that and they're not burning expensive Jet-A they're buring cheap, high sulphur diesel or they're on the powergrid. Also don't have the expense of having an A&P maintain it, and having airworthiness issues.

Quoting Pilotboi (Reply 12): But pilots also need to be in the thought process that having an engine running at the gate is not the best thing to do. No ground movement can take place, no fuel, no unloading, etc. So next time your flying, consider other things that you may not be able to see in the cockpit. I'm not saying that one way is better then the other, and of course each situation has it's own circumstances, but just remember theres more then just you and your captain working on that flight.

No worries, most of us understand that and it is part of out jobs to "consider other things that [we] may not be able to see in the cockpit." In the end, it is the captain and FO that often get to do a carpet dance when something goes wrong.

I also know that there is a lot more happening on the ramp than I would ever imagine as well, so we do our best to accommodate when it is operationally feasible and safe.

Furthermore, I honestly don't want anyone anywhere near the plane when the beacon is on (ie engine running). Those two, six bladed, 13.5 ft diameter props can do some serious damage. We normally have them feathered and cooling down once we put the parking brake on and shutdown approximately 30 seconds later. If ground power is not available we usually figure it out soon there after and just start the APU.

This is rarely an issue where I fly, by the way. I was refering to the OP and why the engines are left running. He is also referring to United mainline where there may be some more other issues, such as frustration with the inefficiency of the operation, that may contribute to some pilots just leaving the engines running instead of starting an APU. It may not matter if they shut down the engines, there might not be anyone to off load bags anyways!

Checko

Quoting TheGreatChecko (Reply 17): No worries, most of us understand that and it is part of out jobs to "consider other things that [we] may not be able to see in the cockpit." In the end, it is the captain and FO that often get to do a carpet dance when something goes wrong. I also know that there is a lot more happening on the ramp than I would ever imagine as well, so we do our best to accommodate when it is operationally feasible and safe.

Great! Some pilots (not you) tend to forget that there are other people working to make their flight possible. I don't want to get off topic, but lately I've had to deal with or be around those pilots/captains.

I notice that our 737s always leave #1 running (in the 8 months I've worked here I've seen one run the APU only twice), while our Airbus and 757s will come in with the APU running and immediatly shut down the engines. Can anyone explain that?

As a side note, we offload bags on the 737s when 1 is still turning. As long as the chocks are in, it's all good.

Quoting Pilotboi (Reply 18): Great! Some pilots (not you) tend to forget that there are other people working to make their flight possible. I don't want to get off topic, but lately I've had to deal with or be around those pilots/captains.

I know how you feel. It can be tough to fly with that kind of captain unless you just stop caring yourself.

Quoting Pilotboi (Reply 18): Great! Some pilots (not you) tend to forget that there are other people working to make their flight possible. I don't want to get off topic, but lately I've had to deal with or be around those pilots/captains.

You tend to look out for the guys on the ground when you spent years throwing bags like I did. I'm usually carrying Cokes or bottles of water from the galley on hot days to offer to the rampers. Had an FO bring me one once on a rediculously hot day, really appreciated it so I try to pay it forward now. We're all there for a common cause.

One of the things that I don't see, or I'm to lazy to notice is engine cool-down periods. The CF-34s on the 170 require a two-minute cooldown at idle before shutdown. On a long taxi this isn't an issue but short ones it can be. The steering is also on the #2 system which is on the right engine. This is one of the reasons we start #1 first and typically shut it down first as well.

Hello

Quoting Pilotboi (Reply 12): They may shut one engine down during taxi in, but I doubt they would shut all down until the aircraft comes to a complete stop. You never know if you'll have to stop a few feet short for something, and then continue taxiing which would require some thrust to get moving again.

Working on long haul I tend to fly on the either the Boeing 744 or the B772 – if I have really upset my OCRM (operations crew resource manager) I’m sometimes forced onto the Boeing 763 (I don't like her much, not to crew on anyway).

I don’t think IV ever heard one of the engines being shut down after landing and taxing on the remaining engine/s. Of course I have been in situations were the engine has been shut down on the ground and in the air for technical reasons (fire, bird stick etc).

When I said some commanders seem to shut down the engines before we stop, they shut both of them down as we are feet away from the stand stop point, you then feel the final breaking before the parked and secured signal is issued to the cabin crew (this is normally the point were PAX try running us over to get off our lovely jet).

On certain stand (ramps) the engines are totally shut down before arrival to the stand and we are tugged in, I guess this is because of jet blast concerns? This happens quite a bit on the Boeing 744 and Boeing 772 at LHR terminal four and noticed it a lot with Continental airlines at their hub in EWR, on certain stands.

Kimberly

Quoting Kimberlyrj (Reply 22): On certain stand (ramps) the engines are totally shut down before arrival to the stand and we are tugged in, I guess this is because of jet blast concerns?

Could be. Could also be that the spot in which the plane is going to park is very small, and they'd rather have a ground crew who know the space well and have a good view of everything that's going on (particularly where the wings are) do the parking rather than a flight crew that may have never been to that airport before and can only see what they can see out the windows (and normally can't tell where the wings are).

-Mir

Hey

Quoting Mir (Reply 23): Could be. Could also be that the spot in which the plane is going to park is very small, and they'd rather have a ground crew who know the space well and have a good view of everything that's going on (particularly where the wings are) do the parking rather than a flight crew that may have never been to that airport before and can only see what they can see out the windows (and normally can't tell where the wings are).

It tends to happen at Heathrow's stands 403, 402 & 401, all of which are around the 'front' (land side) of terminal four, behind is a road and some other equipment so I think it's a jet blast issue, hope the commander knows his/her hub's stands and ramps (but you never know)...

Kimberly.

Quoting Kimberlyrj (Reply 24): It tends to happen at Heathrow's stands 403, 402 & 401, all of which are around the 'front' (land side) of terminal four, behind is a road and some other equipment so I think it's a jet blast issue, hope the commander knows his/her hub's stands and ramps (but you never know)...

At T4 I understand there are also noise restrictions which sometimes require a shutdown and tow in, whichever gate is in use. I've been stuck onboard BA flights arriving early at LHR where we've had to wait for a tow in and it was explained this was due to arriving before a certain time, so the delicate locals don't get woken up too early.

Obviously not everything Captain Speaking says over the PA is the absolute truth but I was inclined to believe this explanation.  

Thinking of unusual engine shutdown practices, I remember one 737-200 operator which regularly used to taxi in without retracting landing flap, then select flap up at the gate as the engines were shut down. I assumed this was done so the hydraulic flow to the flaps depressurised the system, which otherwise would only slowly depressurise.

Hello

Quoting Jetlagged (Reply 25): At T4 I understand there are also noise restrictions which sometimes require a shutdown and tow in, whichever gate is in use

I think this is right at certain times of the early morning and late night, however gates 404 thru 412 my friend who is a Captain says they nearly always taxi in under engine power, but other areas of Terminal Four at LHR where noise is more of a problem tug’s are more regularly used.

It can be a pain for the cabin crew when this happens, PAX hear the engines shut down and ignore the seatbelt sign and just decide it’s time to get off, something that crew can’t stand (this even happens if announcements have been made about what’s going on)

Happy Tugging

Kimberly.

I hear Skybus saves money by hooking a generator to pedals beneath the passenger seats.

Quoting Pilotpip (Reply 16): GPUs are roughly half that and they're not burning expensive Jet-A they're buring cheap, high sulphur diesel

Wrong answer.....
Diesel fuel was mandated for low-sulphur and because of that it generally is $4.00-$5.00/gallon - maybe more.

Jet is usually purchased in extreme bulk or is hedged at alot less than Diesel. Also...most states want that almighty tax dollar so they have made it illegal to use jet fuel in GSE equipment

The airline I deal with pays on average between $3.00-3.25/gallon for jet-a.

KD

Quoting Kimberlyrj (Reply 26): It can be a pain for the cabin crew when this happens, PAX hear the engines shut down and ignore the seatbelt sign and just decide it’s time to get off, something that crew can’t stand (this even happens if announcements have been made about what’s going on)

True and sometimes it is the mere act of coming to a stop which gets passengers jumping up and reaching for the overhead lockers. Even if the aircraft has just stopped to wait for a stand to clear, with the engines running, you get people rushing for the exit. It's annoying for those of us who do listen to announcements too. Sometimes it helps if the captain mentions well in advance whats going to happen before the aircraft stops (and then repeats it for the hard of understanding).

One thing that's worse than people clogging the aisles prematurely like that is people who stand up in the aisles, but then only begin to get their bags down when the exits open and the person in front of them walks off.