Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Your best fuel/cost savings tips

Tech Log The very best in practical technical discussion on the web

Your best fuel/cost savings tips

Old 13th Sep 2018, 21:24
  #21 (permalink)  
 
Join Date: Nov 2010
Age: 56
Posts: 945
Received 0 Likes on 0 Posts
Originally Posted by B2N2


Realy?!
if you burn 30,000lbs of fossile fuel during your trip you really think 300lbs matters?
Its just a feel good maneuver. Virtue signaling.
Switching to NEO engines saves 15%, or in your example 4500#. Even saving 1% in an industry that regularly has 2% margins can make a difference.
hans brinker is offline  
Old 13th Sep 2018, 21:49
  #22 (permalink)  
 
Join Date: May 2009
Location: london
Posts: 137
Likes: 0
Received 0 Likes on 0 Posts
You could save a bit of fuel and a lot of localised pollution if you used towbots to take aircraft from the gate and towed them almost to the hold point so that they minimised taxiing and waiting about with the engines running. Nice autonomous towbots ensuring you only have three minutes from startup to takeoff. Heahrow would love it!
GlenQuagmire is offline  
Old 14th Sep 2018, 01:44
  #23 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 68
Posts: 4,357
Received 157 Likes on 75 Posts
SeaTac airport makes a big deal of having pre-conditioned air and ground power available at every gate so there is no need to run the APU at the gate until you're ready to start engines.
tdracer is offline  
Old 14th Sep 2018, 05:59
  #24 (permalink)  
 
Join Date: Sep 2007
Location: EU
Posts: 155
Likes: 0
Received 0 Likes on 0 Posts
When your flight is fully booked never accept anybody on jumpseat to keep a/c weight low
poldek77 is offline  
Old 15th Sep 2018, 07:15
  #25 (permalink)  
 
Join Date: May 2001
Location: England
Posts: 1,904
Likes: 0
Received 0 Likes on 0 Posts
Learn your three times table
Superpilot is offline  
Old 15th Sep 2018, 11:39
  #26 (permalink)  
 
Join Date: Jan 2000
Location: FL410
Posts: 860
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by hans brinker
Be careful with the directs, we use wind planning for best routes on longer legs. I have seen increases in flight time of 15 minutes after getting a direct (off course we didn't take the direct...).
Be careful comparing directs to original route, as (unless winds are known along/abeam waypoints on direct clearance) the time increment cannot be relied upon.
This is the reason why, when all actual winds are used at waypoints, the ABEAM functions in FMC on NG exists, so not to loose valuable data in case of direct clearance...

An operator entering AVG WIND at first waypoint after TOC does so for preflight planning and estimate of time and fuel on arrival in comparison to flight plan, not for inflight use.
Same operator requiring TOC WIND to be entered (wind after ~20 minutes would be good) does so for optimising fuel burn up to TOC, not for estimate time and fuel on arrival.
Therefore not applying both above upsets the preflight prediction on longer flights with multiple wind changes, giving inaccurate data for crew to work with, showing incorrect times and fuel prior to flight.

If FMC is left unchanged and no actual winds for each waypoint are entered (which could be done when time permitting preflight or in cruise flight), when executing a direct clearance, last known wind (AVG or TOC in prior example) is used to predict from next waypoint and onward estimates, however actual wind at time of execution is used for prediction to next waypoint.

When getting cleared for a direct clearance of an hour, where FMC entered TWC at TOC was ~100kts, but wind at execution of direct is HWC ~100kts a ~40% groundspeed differential is observed in estimate for next waypoint, this equates to ~25 minutes.


Originally Posted by The Old Swedish
On a narrow body you can safe up to 15kgs if you land with a reduced flap setting.
On similar narrow body you can save up to 50-70kg if you land using idle reverse thrust which can sometimes only be achieved by wasting those 15kgs saved through use of lower flaps. (Slow it down +15kgs, ability for landing with idle reverse -70kgs, saving 55kgs!)
Skyjob is offline  
Old 15th Sep 2018, 16:14
  #27 (permalink)  
 
Join Date: Sep 2010
Location: U.S.A
Age: 56
Posts: 496
Received 3 Likes on 2 Posts
Superpilot nailed it.

I suspect I know what tree he’s barking up.

If you are 30 miles to run, flap 2, 180 knots 3000’ with the chicken stick out then you are wasting more fuel than the savings just listed above save.

Seen it too many times in my career, so many pilots totally clueless about altitude versus track miles.
oicur12.again is offline  
Old 15th Sep 2018, 16:27
  #28 (permalink)  
 
Join Date: Aug 2013
Location: blue planet
Posts: 45
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Skyjob
On similar narrow body you can save up to 50-70kg if you land using idle reverse thrust which can sometimes only be achieved by wasting those 15kgs saved through use of lower flaps. (Slow it down +15kgs, ability for landing with idle reverse -70kgs, saving 55kgs!)
Can‘t agree more!
The Old Swedish is offline  
Old 15th Sep 2018, 16:36
  #29 (permalink)  
 
Join Date: Dec 2001
Location: GA, USA
Posts: 3,182
Likes: 0
Received 11 Likes on 8 Posts
Originally Posted by hans brinker
Switching to NEO engines saves 15%, or in your example 4500#. Even saving 1% in an industry that regularly has 2% margins can make a difference.
If they work correctly and don’t need to be shutdown in flight.
Oh wait...that’s probably how they get their 15% savings..
B2N2 is offline  
Old 15th Sep 2018, 16:37
  #30 (permalink)  
 
Join Date: Apr 2008
Location: Nearer home than before!
Posts: 524
Likes: 0
Received 0 Likes on 0 Posts
Agree. also a good one is if you've gone for high speed but get an intermediate level off FFS SLOW DOWN. Keeping the higher speed at low or mid altitudes haemorages fuel like nothing else. Not that ATC gives a hoot....
RVF750 is offline  
Old 16th Sep 2018, 12:19
  #31 (permalink)  
 
Join Date: Sep 2003
Location: away from home
Posts: 887
Received 0 Likes on 0 Posts
Originally Posted by tdracer
SeaTac airport makes a big deal of having pre-conditioned air and ground power available at every gate so there is no need to run the APU at the gate until you're ready to start engines.
Readily available Ground Power and Air is not very common at our US destination. Lots of prolonged APU use. Good on SEA!
oceancrosser is offline  
Old 16th Sep 2018, 21:06
  #32 (permalink)  
 
Join Date: Oct 2010
Location: 5° above the Equator, 75° left of Greenwich
Posts: 408
Likes: 0
Received 0 Likes on 0 Posts
Any one knows what the difference in full consumption is if you modify the descent speed from CI (around 270kias) to say 300 on a medium size aircraft? You'll keep cruise power a few minutes longer but your descent will be shorter, taking advantage of the higher GS/TAS.

I've done this to save a couple of minutes when going behind schedule but don't know how does it affect fuel economy (haven't done the fuel gauges vs computer flight plan math to be honest).
Escape Path is offline  
Old 17th Sep 2018, 14:09
  #33 (permalink)  
 
Join Date: Jan 2000
Location: FL410
Posts: 860
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Escape Path
Any one knows what the difference in full consumption is if you modify the descent speed from CI (around 270kias) to say 300 on a medium size aircraft? You'll keep cruise power a few minutes longer but your descent will be shorter, taking advantage of the higher GS/TAS.
I've done this to save a couple of minutes when going behind schedule but don't know how does it affect fuel economy (haven't done the fuel gauges vs computer flight plan math to be honest).
Work out the fuel flow for your aircraft type in cruise (~2200/2500 kg/hour for 737);
Work out time spent extra in cruise (check against calculated TOD to get minutes extra) then based on above work out additional cruise fuel requirement;
Work out the fuel flow for your aircraft type in descent (~500 kr/hour for 737);
Work out time spent less in descent (use RTA for runway prior and after KIAS increase (earlier arrival therefore time gained, then reduce it by additional time spent in cruise), this gives descent saving;
You WILL find out that a minute extra in fuel in cruise (~40 kg) can only be regained by reducing descent time by >6 minutes which means this was it is to generate a fuel saving.
Starting an idle descent as soon as possible at best glide speed (lowest CI) is most fuel efficient.
Skyjob is offline  
Old 18th Sep 2018, 13:42
  #34 (permalink)  
Drain Bamaged
 
Join Date: Mar 2000
Location: Earth
Age: 56
Posts: 536
Received 25 Likes on 9 Posts
Originally Posted by sonicbum
- minimise taxi time (intersection takeoff)
Really!? Doing intersection takeoff to save fuel?
I guess somebody did the math and figured out that it will still offset the occasional overrun’s cost
ehwatezedoing is offline  
Old 18th Sep 2018, 16:04
  #35 (permalink)  
 
Join Date: Oct 2010
Location: 5° above the Equator, 75° left of Greenwich
Posts: 408
Likes: 0
Received 0 Likes on 0 Posts
Thanks Skyjob, that's quite helpful. Should be interesting to run the math even if you already gave out the answer haha

@ehwhatezedoing

Forget a runway overrun. That's taking it to the extreme. Depending on runway length, current conditions and aircraft weight, you would need to reduce flex to a lower degree to meet perform requirements plus the increase in fuel associated with the increase in power. Unless really light on weight (i.e. no reduction in flex for takeoff) I don't think it would save too much.

P.S. We aren't allowed to do intersection takeoffs at our gig
Escape Path is offline  
Old 18th Sep 2018, 17:03
  #36 (permalink)  
 
Join Date: Jul 2014
Location: Germany
Posts: 344
Likes: 0
Received 0 Likes on 0 Posts
Isn't higher climb power better for fuel consumption?

I would assume the same applies to takeoff power no?
wiedehopf is offline  
Old 18th Sep 2018, 17:33
  #37 (permalink)  
 
Join Date: Jul 2014
Location: Germany
Posts: 344
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by TangoAlphad
Low power to save engine life and then full thrust if you are going to get a continuous climb.
High thrust on ground can cause much higher temps than in flight and temp = $$$.
I thought this thread was about saving fuel cost
Just put a spare engine in the cargo compartment.
wiedehopf is offline  
Old 18th Sep 2018, 17:43
  #38 (permalink)  
 
Join Date: Mar 2012
Location: Having a margarita on the beach
Posts: 2,402
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by ehwatezedoing

Really!? Doing intersection takeoff to save fuel?
I guess somebody did the math and figured out that it will still offset the occasional overrun’s cost
I’ll tell You a secret : we do have performance data for intersection departures without having to gamble.
sonicbum is offline  
Old 18th Sep 2018, 20:51
  #39 (permalink)  
 
Join Date: Jul 2007
Location: Germany
Posts: 1
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by wiedehopf
Isn't higher climb power better for fuel consumption?

I would assume the same applies to takeoff power no?
Fuel critical sector, max rated TO provides lowest burn.

however, cost in terms of engine life are significant so most stick with derate/flex for commercial reasons. unless you have an engine maintainance contract that doesnt mention flex/drt vs Max, in which case, let er rip!!!
VinRouge is offline  
Old 19th Sep 2018, 18:30
  #40 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 68
Posts: 4,357
Received 157 Likes on 75 Posts
Originally Posted by VinRouge
Fuel critical sector, max rated TO provides lowest burn.

however, cost in terms of engine life are significant so most stick with derate/flex for commercial reasons. unless you have an engine maintainance contract that doesnt mention flex/drt vs Max, in which case, let er rip!!!
Several years ago, we were investigating a particular Asian airline that had horrible time-on-wing for their 737/CFM56 engines. Mainly sort haul, they were running out of EGT margin in ~3,000 hours - at a time when the typical operator was in the range of 15,000-20,000 hour time on wing.
Come to find out, they were using max TO every single takeoff - never a derate of any kind. At around a million dollars to overhaul an engine, you'd have to save a whole lot of of fuel to justify an extra two million dollars/year in engine maintenance...
tdracer is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.