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Chuck Dreier

ETOPS/Fuel Question

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I want to fly an ETOPS operation KSEA-PHNL.  Maximum fuel on the PMDG 737-800 is 45,900 pounds.  The required fuel for this trip is 49,165 lbs.  Alaska Airlines flies this route ETOPS daily.  My question is whether there's a way to make an adjustment in the PMDG 737-800 to extend the fuel load?  If not, that eliminates quite a bit of my long route plans.  Thanks guys!

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Most of the AS flights leave with between 38,000 and 41,000 pounds on the Hawaii routes. And that's with full seats.

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I'm using PFPX and it's showing enroute fuel of 32,009 plus extras including alternate totaling 44,345 lbs.. I reduced payload to 85 PAX and that puts me about 21,000 pounds underweight. I think I've got to go back and do some resetting in PFPX. It is giving me warnings about load that I've not seen before.

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I use PFPX as well, but only for the 777.  Something looks funny with the way its planning your extra fuel.  Whats your alternate?  For HNL, OGG would be a normal planned alternate.

 

For exsample.  Tonights SEA-HNL flight (Flt 853) has 43,456 pounds planned (due to headwinds) with a ZFW of 130.4.  That included full pax and 4590 lbs in the pits.

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What is the planned engine out fuel burn per hour at the lower altitude ? Can PFPX plan the fuel for this complex route and alternates ?

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To my knowledge, the type that ASA flies is the exact same as the one we've modeled (none of the AUX tank options, etc etc). Instead of immediately jumping to the conclusion of "I must change something in the config files because it was modeled differently/incorrectly" I think it's usually more prudent to have a look at your own process. If one is not a pilot or a dispatcher, the natural first tendency should be to think: "okay, there's something I'm missing here." I have a feeling that's some of why you're here asking, but the wrong question is being asked.

 

When it comes to aircraft, the usual situation is: you can have full fuel, or full passengers, but not both. Looking at ASA's reported average passenger load factor (85%), one can see they are not usually operating with full flights. Now, obviously even if it were true that the PHNL leg were full, mainline legs could pull this number back, which is just how averages work. However, keep in mind that when you press the limits of an airframe, you're going to have to make sacrifices. If the wind is stronger one day, you're going to have to pull back on payload to bring extra fuel, which means that you're leaving passengers behind sometimes. In the winter, the wind gets pretty bad at altitude. Right now in the Central US, it's howling at about 110-115. It's not as bad out over the ocean, but the potential exists.

 

Additionally, PFPX (and most other programs) are not randomizing the load based on the route. This means that it might be adding a bunch of cargo on a route where you might not fly much/any cargo. If you assume that each passenger is bringing 1.25 (averaged) bags at 35lbs, then a full ASA flight (157-160 seats) is going to have about 7000lbs of stuff down in the bin. As a fact of airline life, cargo makes a lot more than passengers do, so if it's a choice between taking cargo and taking a person, the cargo usually wins, but I'm doubting ASA has a huge cargo haul between SEA and HNL (especially when Hawaiian and Delta are dragging a 330 and a 757 down there daily).

 

ASA has an ETOPS 180 rating for their 73s as well. If you planned with 120, then your route could have been affected. Additionally, the amount of fuel carried is dependent on the scenario you chose. One Engine Decompression means a lot of low flying, which eats fuel as if it were turkey and stuffing on Thanksgiving day. Planning for just one engine (not decomp) doesn't cover your bases as much, but to lose an engine and your pressurization is a very rare event, and planning without the decomp means you have less of a fuel requirement.

 

Check your fuel policy as well. As the flight is not wholly contained in the 48 domestic states, it needs to be US Flag Jet ("international" for all intents and purposes). Still, I believe the US fuel policy is more lenient than the EU/ICAO versions.

 

Finally, check your alternate. You could probably use PHNG to avoid trying to get over to another island. Keep in mind, though, that you do NOT need an alternate if:

  • For a flight less than 6 hours*, if, for a period of 1 hour before, to 1 hour after,
    • The ceiling is 2000' AFE or greater, or 1500' above the lowest mins, and
    • The visibility is 3sm or greater, or 2sm above the lowest mins

Not filling an alternate when you do not have to will save on this requirement, as well. The above reference is 14 CFR §121.621 (or "FAR 121.621").

 

*FlightAware and the ASA website likely list the DOT times as 6 hours and change. The planned time is likely somewhere around 5.5, depending on wind. Remember that, for the purposes of meeting regs, your flight time is how you plan it on the dispatch paperwork. If PFPX estimates less than 6 hours, then you're set. DOT times are only good for on time performance stats, which is why they're usually padded so that you land 'early'.

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You could try a re-dispatch using PFPX. I am not sure how effective that would be but you could try it anyway. All you need to do it click on a button and PFPX will do the rest. Or you could buy the T7.

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Kyle, don´t ETOPS regulations require the airline to plan for fuel at the one engine decomp ?

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I've flown quite a few ASA aircraft completely full between the islands and Seattle IRL. We'd make a tech stop in the Bay area before sacrificing payload; something I've never had to do and which typically only happens a few times per winter. Re-dispatching an hour out of destination is another option.

 

I once took that day's real-world flight release and flight plan from SEA-KOA and flew it in the ngx - time accelerating to 16x between waypoints of course lol (works fine straight and level out over the ocean, no scenery). Burns and times were within RW margin of error... within a few minutes and few hundred pounds at destination. So I'd say PMDG's modeling is pretty darn good. This has to be a planning issue like Kyle says; either with PFPX itself or with the rules you're dispatching under.

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Kyle, don´t ETOPS regulations require the airline to plan for fuel at the one engine decomp ?

 

As Kyle said you are require to have enough fuel even for 1EO + Decomp, the 3 scenarios that are required for ETOPS briefly are:

 

1- All ENG with Decomp. (10.000ft)

2-1EO with Dcomp. (10.000ft)

3- 1EO without Decomp (Driftdown altitude), Drifdown as you cannot maintain the same altitude with just One Engine.

 

All these calculations + APU running and 10% for icing, these calculations are based on the worse case scenario that 99.99% never gonna happen, if you end up needing more fuel to meet those requirements its gonna be added into ETOPS reserve.

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All these calculations + APU running and 10% for icing...

Just a heads up, almost all of ASA's ETOPs flights are now APU on demand, so you don't have to run the APU the whole way. Honestly unsure if fuel planning assumes that or not though.

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I was talking about the fuel calculation consideration and that's a requirement, surely they don't run it all the way.

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Kyle -That was a very thoughtful and great post.  Thanks for taking the time.

 

 

To my knowledge, the type that ASA flies is the exact same as the one we've modeled (none of the AUX tank options, etc etc). Instead of immediately jumping to the conclusion of "I must change something in the config files because it was modeled differently/incorrectly" I think it's usually more prudent to have a look at your own process. If one is not a pilot or a dispatcher, the natural first tendency should be to think: "okay, there's something I'm missing here." I have a feeling that's some of why you're here asking, but the wrong question is being asked.

 

 

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I was talking about the fuel calculation consideration and that's a requirement, surely they don't run it all the way.

Actually we did for a while as an intermediate step of certification, until we had enough data to prove our APUs would start reliably when cold-soaked. Wasn't sure if that was what ya meant.

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As Kyle said you are require to have enough fuel even for 1EO + Decomp, the 3 scenarios that are required for ETOPS briefly are:

 

1- All ENG with Decomp. (10.000ft)

2-1EO with Dcomp. (10.000ft)

3- 1EO without Decomp (Driftdown altitude), Drifdown as you cannot maintain the same altitude with just One Engine.

 

All these calculations + APU running and 10% for icing, these calculations are based on the worse case scenario that 99.99% never gonna happen, if you end up needing more fuel to meet those requirements its gonna be added into ETOPS reserve.

 

Thanks for clarifying that sir. I dream of making my own ngx ETOPS flight to Hawaii by the book and completely legal release. Still a ways away obviously.

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I was a pax on a Continental B737-700 KSNA-PHOG, and I've simulated numerous B787/738 flights from multiple locations to/from the islands using PFPX and never had a problem with the planning.

 

The flight I took was memoriable because there were more people in 1st Class than coach, we had our choice of almost any seat or row for that matter and the sunset enroute was startlngly beautiful. I say almost any seat because the attendent would not allow you to sit in a "extra cost seat" unless you paid the additional fee LOL. She was nice enough to show us how to use the seat cushion as a pillow.

 

Don't forget to use the fuel crossflow in the last hour of flight, there's also some electrical checks but I'm not up on those.

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Actually we did for a while as an intermediate step of certification, until we had enough data to prove our APUs would start reliably when cold-soaked. Wasn't sure if that was what ya meant.

 

This is something that gives more reliability to the APU which is always a good thing, and it does not affect what was said in my previous post, ETOPS fuel requirements remains the same until there will be a change in that regulation.

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Out of curiosity - assuming you're using the latest version of PFPX (1.23), what flight levels are you getting throughout the flight?

 

Do you have anything selected in the "Optimisations" section? It defaults to "Fuel" -- but in my experience it is buggy and usually results in holding you down at extremely uneconomical levels for long periods of time. Try selection "None" from the dropdown (should grey out the little green light) and re-run the calculations: you might be pleasantly surprised.

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I want to fly an ETOPS operation KSEA-PHNL.  Maximum fuel on the PMDG 737-800 is 45,900 pounds.  The required fuel for this trip is 49,165 lbs.  Alaska Airlines flies this route ETOPS daily.  My question is whether there's a way to make an adjustment in the PMDG 737-800 to extend the fuel load?  If not, that eliminates quite a bit of my long route plans.  Thanks guys!

When you have a chance could you provide me with your payload or ZFW.

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This is my PFPX output using the upcoming 0330z departure 9/23/2015 of Alaska 893 and today's real world routing:

HAROB5 HQM SEDAR 4200N 13300W 3900N 13700W HELOP A332 AUNTI R463 APACK MAGGI3

FUEL ENDUR
TRIP 34650 ........ 05:45
10 PCT 3120 ........ 00:34
ALTN PHOG 2320 ........ 00:21
INTL HOLD 2393 ........ 00:30
ETP ADD 1448 ........
MIN T/O 43931 ........ 07:10
EXTRA 0 ........ 00:00
TAXI 520 ........ 00:20
RELEASE 44451 ........ 07:30

ZFW TOW LDW
MAX 136000 174200 144000
PLN 130269 174200 139545

That is 35,490lbs of payload using a DOW (dry operating weight) of 94,779lbs. and the maximum MTOW Boeing offers on the -800 of 174,200lbs.

Not bad for a 2,563nm (air distance) trip. Almost 200nm greater than the flight-plan distance due to the 33kts of average headwind (forecast).

ETOPS alternates used are (KOAK and PHNL) and using ETOPS 180 with 1185nm maximum diversion distance.

Remember, in the real world Alaska Airlines will carry more payload / lbs of fuel than we will be able to with the PMDG -800! Why?

They are currently going through with the split scimitar retrofit on most of the -800s and all of the -900ERs. Over this trip length a SSW fitted -800 will burn ~2% less block fuel (impressive!) than a blended winglet fitted -800 (as modeled by PMDG). That would result in a ~880lbs block fuel reduction on this flight (more weight for payload).

The U.S. Flag (Jet) fuel policy doesnt make matters better considering the 10% F.A.R. reserve requirement... Many international operators, under EU-OPS and others such as Emirates, Cathay, British Airways, KLM etc. have been using statistical contingency fuel for many years now (very successfully).

In essence they track individual contingency burn over hundreds/thousands of flights on each specific route and then they load contingency fuel to cover 90/95/99% of those flights.

This of course means the statistical contingency figures change on individual routes as the time of year changes and thus the weather etc. Beats having to carry around 5% or 10% like the U.S. carriers have to. At least the F.A.R/s allow in-flight re-dispatch, which allows the 10% requirement to be reduced significantly as it is calculated from re-dispatch point to final destination. That of course is not a option on this specific route, due to the obvious lack of en-route/re-dispatch alternates.

I have heard the FAA will finally move towards a new policy called performance based fuel (different name for statistical contingency). Something the major U.S. operators have long been pushing for, especially the ones such as United, AA, Delta who have to carry thousands of pounds of extra contingency fuel under current regulations. This will of course come with many valid requirements such as tracking individual aircraft burn, route performance etc. (which I'm pretty sure all three already do to monitor aircraft/engines etc.).

In any case, ~35k + payload is a full 160 seater -800 with crew, bags, pantry etc.



Also do not forget about the ETOPS 180 distance you have set in the aircraft profile within PFPX.

Different operators will choose difference maximum diversion distances for 60/120/180 minutes on the 737NG.

For example, one U.S. 737NG operator uses 1185nm as the ETOPS180 distance on their -700/800. Another U.S. 737NG operator uses 1080nm.

Why the difference?

The operator using the latter, and lower figure for planning purposes, does not require more and hence avoids having to carry the extra 105nm of ETOPS critical fuel (when critical fuel is needed) to cover for worst case scenarios (1 engine out, 1 engine out + depress. and depress only). The operator using 1185nm needs the extra 105nm for certain routes. There is of course a maximum still air 1EO distance for each ETOPS aircraft. It is up to the operator and its needs to determine if it needs and wants to plan up to the full capability.

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