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Taxiing To Run Way And Fuel Use  
User currently offlineUltrapig From United States of America, joined Dec 2003, 590 posts, RR: 0
Posted (6 years 5 months 4 days 22 hours ago) and read 3500 times:

I was at ORD today and my flight left around 12:30 pm. Once we left the gate it took about 25 minutes to take off. Not really so bad and I'm not complaining but my question-with the price of fuel why doesn't ground control release planes from gates so that the sitting takes place at the gate with the plug in instead of the engines running on the taxiway? In short why not time it so there is a four or five plane line at the runway instead of 20?

I'm sure someonecan tell me why this is a stupid idea? I do know that planes generally have to leave the gate with engines on to be inline for takeoff but why not change the policy.

9 replies: All unread, jump to last
 
User currently offlineDualQual From United States of America, joined Mar 2006, 788 posts, RR: 1
Reply 1, posted (6 years 5 months 4 days 22 hours ago) and read 3484 times:

Typically this can be done in times of a large push with big delays (often at EWR). The flip side is that depending on the time of day odds are the airline will need the gate for an inbound flight. Any savings that might result will be offset by the inbound out burning fuel waiting on the gate and the cost of rebooking missed connections.

User currently offlineMir From United States of America, joined Jan 2004, 21801 posts, RR: 55
Reply 2, posted (6 years 5 months 4 days 20 hours ago) and read 3447 times:



Quoting Ultrapig (Thread starter):
In short why not time it so there is a four or five plane line at the runway instead of 20?

Because when 20 planes are scheduled to depart during the same five minute span, you're going to have a 20 plane line at the runway. So select five of them to go and have the others wait at the gate, perhaps? Sounds good, but the other fifteen are going to start intruding on the space set up for the 15 planes that are scheduled to depart right after that. And the delays start mounting from there. Add in the fact that keeping planes at the gate means keeping planes that are waiting for that gate out on the taxiways with their engines running, and the fuel savings start to drop.

Also, the logistical nightmare to meter airplanes from different places on the airport to the same runway, arriving at pretty much the same time, makes it operationally impractical.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineCX flyboy From Hong Kong, joined Dec 1999, 6626 posts, RR: 55
Reply 3, posted (6 years 5 months 1 day 16 hours ago) and read 3224 times:

At an airport like Hong Kong, with a simple layout of taxiways and terminals it is easy to see why they do this.

Recently there has been a lot of bad weather passing through Hong kong, and whenever there is lightning near the airport, ground operations come to a stop as ground crew take cover. The effect is that departures slow to a standstill and very soon all the gates at the airport are occupied and there is a long queue of landing traffic parked waiting for their gate.

What you are suggesting is a good idea, but unfortunately not practical at a busy airport. Most of these large busy airports are running near, at or beyond capacity and it is a real tight juggle arranging landing and departure slots and vacant gates. Unfortunately efficiency takes a backseat just to keep the show running.


User currently offlineChrisMUC From Germany, joined Jul 2006, 66 posts, RR: 0
Reply 4, posted (6 years 5 months 1 day 10 hours ago) and read 3179 times:



Quoting Ultrapig (Thread starter):
why doesn't ground control release planes from gates so that the sitting takes place at the gate with the plug in instead of the engines running on the taxiway?

that's exactly what is done at MUC and FRA and is supposed to be introduced in the entire EU. Although we're not happy when we've to wait at the gate during peak hours, I think that it works quite well in the meantime (at least at MUC). At the beginning taxi time was misjudged quite often by ATC but now they manage pretty well that there are always about 3 to 5 aircraft waiting at the runway for line up.
On a regular day (no TS) start up delay during peak hours is not more than 10 minutes, so blocked gates are not (yet) a problem.

Quoting Mir (Reply 2):
And the delays start mounting from there

the delay is still the same, whether you wait at the gate or at the runway. Only inbound traffic is a problem if an airport doesn't have enough gates.


User currently offlineUltrapig From United States of America, joined Dec 2003, 590 posts, RR: 0
Reply 5, posted (6 years 5 months 1 day 6 hours ago) and read 3151 times:

Followup question-Understood that gate usuage is very important. But at what point would it make sense for airlines and airports consider equiping "bullpen" areas with hook up so planes could be towed there and parked whiled hooked up waiitng for deaprture with no engine running.

An let's say on a 737-700 for example how much is the fuel flow with the engines just idling compared to crusing?

Can a plane in a very long line sut of one engine during the wait ala the taxiing to gate procedure?


User currently offlineCoolGuy From United States of America, joined Jan 2005, 414 posts, RR: 0
Reply 6, posted (6 years 5 months 1 day ago) and read 3114 times:



Quoting Ultrapig (Reply 5):
airports consider equiping "bullpen" areas

Like the "ballpark" at EWR. Planes also go to a spot on an out-of-use taxiway and just sit with the engines off. It seems that engines are shutting down on the ground more often these days. When's the breakeven point in terms of cost or efficiency between shutting down and remaining on (in terms of minutes of expected wait).


User currently offlineMir From United States of America, joined Jan 2004, 21801 posts, RR: 55
Reply 7, posted (6 years 5 months 13 hours ago) and read 3064 times:



Quoting Ultrapig (Reply 5):
Followup question-Understood that gate usuage is very important. But at what point would it make sense for airlines and airports consider equiping "bullpen" areas with hook up so planes could be towed there and parked whiled hooked up waiitng for deaprture with no engine running.

The areas exist, and are used as holding pads, but getting GPU or air conditioning out there would be difficult - those need some sort of infrastructure to support them. Also, you're going to need a ground crew to connect them, and you're going to have to have the connection points, the placing of which may require a pushback out of a parking spot (which means more ground crew).

Quoting Ultrapig (Reply 5):
Can a plane in a very long line sut of one engine during the wait ala the taxiing to gate procedure?

Absolutely. And they do. At most airlines the standard procedure is to taxi out on one engine and start the other when you're getting close to the end of the line so that it has about five minutes to warm up before takeoff. If the line isn't moving anywhere, planes will shut both engines down.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineDispatchguy From United States of America, joined Jan 2006, 1249 posts, RR: 2
Reply 8, posted (6 years 5 months 5 hours ago) and read 3029 times:



Quoting Ultrapig (Reply 5):
An let's say on a 737-700 for example how much is the fuel flow with the engines just idling compared to crusing?

I dont know the 737-7 taxi fuel flow off hand, but a B767-300 is around 44 lbs/min.



Nobody screws you better than an airline job!
User currently offlinePilotpip From United States of America, joined Sep 2003, 3152 posts, RR: 11
Reply 9, posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 2984 times:



Quoting Ultrapig (Reply 5):
Followup question-Understood that gate usuage is very important. But at what point would it make sense for airlines and airports consider equiping "bullpen" areas with hook up so planes could be towed there and parked whiled hooked up waiitng for deaprture with no engine running.

An let's say on a 737-700 for example how much is the fuel flow with the engines just idling compared to crusing?

Can a plane in a very long line sut of one engine during the wait ala the taxiing to gate procedure?

The problem with the power idea is now you have to staff this remote area as well as equipping it. I don't see that as a viable option.

The penalty box at ORD gets used a lot. Single engine taxi is not only encouraged, but it's SOP for us. Of course, there's the stipulation of abnormal situations which still gives the captain authority to fire up both. We have to let the engines run for at least two minutes after landing for cooldown. My normal flow for things is to shut down #2 when the captain prompts me (or I ask) and fire up the APU as we get about 5 gates away from ours. If we end up going to the box, my job is to start coordinating. I get on with ops, find out how long it's going to be. If it's going to be quite a while the captain may elect to fire up the APU and shut down the engines (I'll get to that in a minute) becuase the APU burns much less fuel. Once in the box, we usually wait for ramp or ops to call and tell us the gate is open. If it's been a while, I make a note of what gate we're going to and try to listen for it. If we have the engines shut down we'll fire one up and when the other aircraft calls for push. By the time they call for taxi we're ready to go and all is well.

Some rough fuel figures for the ERJ-170
Engines Idle- 550pph (per engine)
Cruise 1800-2000pph (per engine)
Breakaway thrust 800-1000pph (single engine)
APU 175 pph

As you can see, it's to our advantage to go single engine or even APU when we're sitting for a while. Better yet, I'd much rather use the GPU and ground air but at some stations (IAD) you're going to have a hard time talking the ramp into hooking up the A/C. This time of year if they don't hook it up, we're leaving the APU running because at some point passenger comfort becomes a bigger issue than fuel savings.



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