9V-SPJ From United States of America, joined Dec 2000, 757 posts, RR: 0 Posted (10 years 7 months 3 weeks 6 days 14 hours ago) and read 10806 times:
I recently flew delta about 4x - ATL-JFK, JFK-CVG, CVG-ATL and most recently ATL-LAX. I noticed that on every single flight, the crew taxi on one engine, and when they near the departure runway, the second engine is started up. Same happens right after landing, one engine is shut down while the other is used to taxi with. Is this a fuel saving move? When did they start this practice? Also, I flew home to LA on DL603, a B762, and I noticed that while taxing on one engine, the crew had to use a significant amount of power to keep us moving. Is he saving fuel in the long run?
Just found this to be a bit odd.
Ngr From United States of America, joined Apr 2001, 176 posts, RR: 0
Reply 2, posted (10 years 7 months 3 weeks 6 days 14 hours ago) and read 10736 times:
I noticed the same thing when I flew on Delta over Thanksgiving. I flew BHM-ATL-CAE and CAE-ATL-BHM on MD-88s and 737-200s, and on 3 of the 4 flights we taxied on 1 engine. I wondered the same thing about fuel saving, because when until the 2nd engine was started, the pilot used a lot more thrust than I am accumstomed to. I flew on Delta in August and they taxied on both engines for all flights.
LH423 From Canada, joined Jul 1999, 6501 posts, RR: 53
Reply 5, posted (10 years 7 months 3 weeks 6 days 13 hours ago) and read 10698 times:
I noticed this as well on my last AA flight, BOS-FLL. I didn't even notice until we were getting to the end of the take-off queue and then I heard the other engine start up. I thought that it was awfully quiet considering we were sitting in row 28 on an MD-80.
« On ne voit bien qu'avec le cœur. L'essentiel est invisible pour les yeux » Antoine de Saint-Exupéry
Juanchie From United States of America, joined Jan 2004, 190 posts, RR: 0
Reply 8, posted (10 years 7 months 3 weeks 6 days 13 hours ago) and read 10625 times:
Let's also keep in mind this has another benefit. By taxining on one engine, you save on engine rotations. In the long run, the engines will last longer and there is no need to run two engines when one will do.
God, forgive me for who I am, and help me be the man I want to be.
Flyibaby From United States of America, joined Aug 2004, 1020 posts, RR: 5
Reply 9, posted (10 years 7 months 3 weeks 6 days 13 hours ago) and read 10534 times:
I'm pretty sure that all airlines are doing this now, even the APU useage. The exception is with SW probably because their pilots fly down the taxiway. I used to think it was to be ontime or to give their ramp crews extra time to turn the aircraft, but then I found out it was because the pilots are only paid by how long the trip is scheduled, not how long it takes them. So by taxiing fast they can try and stay below their hours per month and pick up a few additional trips per month.
Flyibaby From United States of America, joined Aug 2004, 1020 posts, RR: 5
Reply 10, posted (10 years 7 months 3 weeks 6 days 13 hours ago) and read 10522 times:
I forgot to mention, Independence did a study on this, and found that it costs $1 a minute to run the APU instead of groundpower while parked at the gate. With an engine turning on the ground, about $5 a minute. Therefore the costs savings, and this is just based on the CRJ.
Atrude777 From United States of America, joined Aug 2003, 5717 posts, RR: 51
Reply 13, posted (10 years 7 months 3 weeks 6 days 12 hours ago) and read 10432 times:
This engine cutting process ting did start with Delta Express, when they were using Boeing 732's. A pilot noticed how unneccesary it was to use both engines. They were trying to figure out ways to turn arund faster. So they decided as soon as the 732 landed they would switch the right engine off, and taxi on the left so when they got to the gate the ground people could immediatly go to the plane and start taking the bags off without having to wait for the engine to stop for fear of being sucked in. They saw how much time this saved so Delta decided to try it out to the rest of the fleets. Then other airlines caught on. One would think this would be something WN thought of, but as someone pointed out it doesnt benefit them.
Good things come to those who wait, better things come to those who go AFTER it!
57AZ From United States of America, joined Nov 2004, 2586 posts, RR: 2
Reply 16, posted (10 years 7 months 3 weeks 6 days 11 hours ago) and read 10336 times:
The amount of thrust required to taxi is low enough that there is no difference in handling characteristics. Older jet aircraft often taxied on one or two engines but the procedure specified which engine could be used due to design limitations. I believe that the modern systems on twins can usually be driven by either engine. However, on older jets that usually was not the case.
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
OttoPylit From , joined Dec 1969, posts, RR:
Reply 17, posted (10 years 7 months 3 weeks 6 days 11 hours ago) and read 10256 times:
Atrude777 has it correct. During the mid-90's, Delta asked employees for suggestions in saving money. Pilots suggested that taxiing in on one engine, then taxiing out on the other would save time, but also keep the time on each engine the same. It worked and I assume for the most part is still used successfully. It really doesn't take that much more power to get the plane moving and any more that is used can be backed off once the plane's inertia is pushing the plane along.
Also, when it comes to taxiing a plane, as long as its at slow speeds, the assymetric thrust won't affect the plane any. It's only at higher speeds will the thrust start to interfere with the planes movement.
Crosswind From United Kingdom, joined Nov 2000, 2621 posts, RR: 57
Reply 19, posted (10 years 7 months 3 weeks 6 days 10 hours ago) and read 10188 times:
We evaluated taxiing one one engine last year, with mixed results;
For the A320/321 fleet this became an approved procedure after landing only, saving both fuel and brake wear, as the A320/321 have quite a lot of residual thrust at idle so braking is required with both engines running to keep the aircraft at a safe taxi speed.
For the B757/767 fleet it was rejected. The heavier weights of these aircraft meant that you need to apply a fair amount of thrust on the live engine break away from a standstill, and more thrust than normal to keep the plane moving, negating any other savings you might make. Also the GE-CF6 on the B767 requires a 5 min reccomended cooldown period after landing before shutdown.
It was felt undesirable to delay engine startup on departure for any aircraft in the fleet. Starting all engines on pushback provides some degree of warmup, and also problems that can occur after startup may not always be apparent to the crew, and may not become so until the aircraft has commenced it's takeoff run. For example a fuel leak from within the engine would be reported by your pushback crew, but if you start that same engine at the holding point, there may well be nobody to see it...
AV8AJET From United States of America, joined Sep 2003, 1396 posts, RR: 1
Reply 20, posted (10 years 7 months 3 weeks 6 days 10 hours ago) and read 10190 times:
We even taxi on one engine at ASA in DFW & ATL especially due to the long taxi time and long lines. We do it when we can, not only does it save fuel but also slows the taxi speed down so you don't have to "ride" the brakes.
IMPORTANT QUESTION: How can a plane taxi with asymmetric thrust??
Power steering helps overcome this, no big deal really.