Fuel miscalculation with PMDG 747v3 and PFPX

[B777ER 2,486]

9 hours ago, tooting said:

funnily enough of our our a/c's couple of weeks ago had to to do a pan into JFK.  (I was working that day it caused a right old ruckus in the office as we had senior management in observing that day as it was the bad weather they had in NY.) 

On approach they where changed runways 4 times from the handover on the 3rd time the skipper said "if you change us again we will have to pan" a few minutes later they changed and he panned. The ASR that came in for makes for brilliant reading , We get loads of ASRS for the place

JFK is an unmitigated disaster. The FAA is owned investigating the snow storm disaster from a couple weeks ago. See, the problem is each terminal is run like it's own little airport. T5 has no clue what T4 is doing, same for the rest. Tons of empty buildings sitting unused all over the field, hangars that have not been used in decades, etc... So lack of hard stands and busing people is impossible during IROPs.  PANYNJ spent 4.1 billion on the subway under the new Freedom Tower while JFK rots. Needs to go private as PANYNJ is utterly inept. Nothing will change. 

[B777ER 2,486]

On 1/16/2018 at 11:03 PM, JumboJet said:

Good day !

This night I wanted to fly my PMDG 747 between Tel Aviv and New York, as usually I launch my P3D, then Active Sky 4 that I use for the Simulator weather and PFPX (My PFPX server subscription expired some weeks ago I maybe should buy a new one to solve my problem) and finally I launch PFPX for my flight plan.

I've never had any issues with the fuel calculation using PFPX (ok sometimes 1000 or 2000 lbs differences between calculation and fuel at arrival but not more), this night I had a miscalculation of 80,000lbs. The release was about to 283,000lbs and I had an insufficient fuel with 0,0lbs at KJFK all winds and route was in the FMS. 

 

So I've decided to change my fuel by myself before departing (I don't like the idea to swim in the Atlantic for the rest of the flight) and I was very surprised when I've discovered that, to get my 36,000lbs at KJFK I needed 350,000lbs.

I say again I've never had this kind of problem, my last flight RCTP - EDDF with the 747 was fine.

Sorry for my English I'm French.

Thanks by advance if you have a solution or a way to find a solution.

 

Go to the PFPX forum over at Aerosoft and download the fuel profile that is listed there. I use that and usually within 5k lbs on arrival. I also found that using PFPX aloft wind data for planning and ASP4 for wx engine results in very close aloft winds encountered. My EET at each WP is within 2 min of planned. 

[BlueStar 323]

These folks have some good profiles for PFPX.

http://airlinerperformance.net/

blaustern

[B777ER 2,486]

1 hour ago, Bluestar said:

These folks have some good profiles for PFPX.

http://airlinerperformance.net/

blaustern

Was using them. They ate good for the 777 and 737. For the GE and PW 744 they are terrible. Fuel calculations way off when using these. There is another chap goes by "inlovewithboeing" or something similar and his are more accurate than that websites for the 747.

[PinkPony 171]

On 1/17/2018 at 0:52 AM, SAS443 said:

Since PMDG recommends landing with at least 30.000lbs of fuel (13.600kg) because the HYD. Pumps are cooled by the fuel in the tanks, I usually tell PFPX that I want to have that amount of fuel left when I arrive. 

The only caveat (maybe I am doing it wrongly) is that the technique above seem to have null influence over release fuel with re-dispatch?

There has never been a minimum fuel quantity (for hydro cooling) referenced in the FCOM/QRH.

Only the -400 AMM (Aircraft Maintenance Manual) refers to a minimum fuel amount, for hydro cooling.

NOTE: If there is sufficient fuel in the applicable tank, there is no time limit on the operation of the hydraulic pump. If there is less fuel than the quantities below, then the hydraulic pump operation is limited to 15 minutes.

NOTE: The fuel weight values given below are found on a specified fuel density of 6.7 pounds for a gallon (0.802 Kg for a liter).

(a) For system No. 1, there must be 2000 pounds (900 KG) of fuel in the No. 1 main tank.

(b) For system No. 2, there must be 5400 pounds (2450 KG) of fuel in the No. 2 main tank.

(c) For system No. 3, there must be 5400 pounds (2450 KG) of fuel in the No. 3 main tank.

(d) For system No. 4, there must be 2000 pounds (900 KG) of fuel in the No. 4 main tank.

So anytime you are running the pumps with less than <6700kgs total, you are subject to the above limitation.

Considering typical reserves of 8000-9000kgs (assuming 30 minute reserve + 30 minutes to alternate), you will rarely approach that value. Again, not mentioned in any FCOM/QRH, and pilots do not reference the AMM...

 

 

[skelsey 765]

Exactly - as Leo and Ian have pointed out, this thing about the hydraulic pump cooling is, to borrow a word that PMDG like to use, a gigantic simism. As far as I am aware there is zero impact from a flight operations point of view: if it were a concern in flight then Boeing would reference it in the flying manuals, which they do not. 

It is however, as Leo says, in the maintenance manual - because it may be an issue for engineers who may be doing odd (in the context of normal in-flight operation) things with the hydraulic systems - like running the pumps for extended periods - during the course of testing/maintaining them.

With regard to the OP's question: it is always worth 'sanity checking' fuel figures. As a guide, with RR engines at least you can expect a good 10 tonnes per hour fuel burn in flight (more initially at higher weights but decreasing as the flight goes on) plus taxi/contingency/reserve/alternate. If your figures from PFPX (once you have calculated your expected fuel by multiplying the enroute time by 10) are wildly off then you have a problem. 

However, if that figure is closeish to what PFPX had calculated then the issue is likely not that PFPX has the wrong consumption rate and much more likely that the error is in the calculation of flight time (ie an issue with the wind input in to PFPX).

[SAS443 1,723]

@calzonister big thanks for the info!

This is what you get for following the pmdg tutorial 😁

[DEHowie 269]

19 hours ago, iwebber said:

Easy Tiger, there are no hydraulic pumps in the fuel tanks and the airline has been operating this type for over 25 years, do you know how many hydraulic pumps they've lost due to low fuel? The answer rhymes with hero.

Even the company doesn't give us minimum contingency going into JFK and I've yet to fly with anyone who doesn't take more.

No, you have 30 minutes reserve and your diversion fuel + whatever contingency you didn't burn in the go around, that could still be quite a bit. As to another tech problem, of course it's possible, but where do you draw the line. You've already had one unexpected incident, chances of another one? how about another? And another? You can't take enough fuel for every situation... what about if the wings fall off? eh? what about it? what would you do then, punk! you and your cowboy airline... Get's a bit silly doesn't it.

Our system gives us 95% statistical contingency fuel which means the company plans on enough extra fuel to cover 95% of all the extra fuel other flights to that destination, around that time at that time of year burnt. 95% of the time it's enough. As pilots, we're there to try and identify whether we think there's something going on that pushes us into that top 5% where we need more, in JFK, there usually is, so more is taken.

Most of the time we don't hold and there is minimum delay (even into JFK), not touching most of our contingency and our diversion and reserve fuel, in fact, the only place we hold with any certainty is LHR and most of our contingency gets burnt on the ground at LHR waiting to take off.

If we'd taken the fuel the company told us to or more there would be no issue, except for arguing over who fills out the ASR and if by some quirk they wanted to talk to us about the event then biscuits would be provided.

This is all perfectly normal, legal and sensible, I'm stunned someone who actually flies can find a problem with it, are you sure you're not a journalist?

Just trying to add some calm, hyperboleless (real word?) real life info,

Ian

I guess the difference is you assume that turning up with 30 minutes gas is ok because 95% of the time it all works out? What about the other 5% of the time?

You missed the point of my post entirely as it was regarding turning up with 12 tonne of fuel...not 12 tonne plus an alternate plus contingency. So maybe tiger you should read my post again then reasses what your 12 tonne minus an alternate plus contingency equals...

I find it hard to believe in an industry where we plan for the worst case your happy to assume everything will be fine when things start to go wrong.

You assume airlines all carry alternates which in many countries they do not nor is there a requirement. So you do turn up with your 30 minutes plus whats left of your 5% or you have been planned to an alternate less than 5 minutes flying time away which would very easily be affected by unforcast conditions just as easily as your destination.

Anchorage and Elmendorf immediately to mind.

I think the hyd pump cooling has been covered nicely...thanks.

Feel free to be comfortable turning up to an airport with 30 minutes plus 5 percent of your last critical etp so about another 7-12 minutes because you know you never get unforcast weather, you never get un unplanned runway closures, you never get unforcast weather, you never have to go around and you always get your optimum flight levels oh and apparantly you never hold and your aeroplane will never break...nice how did you organize that? 

Meanwhile in the real world i have had numerous unforcast weather events, runways close, alternates go down with weather, aircraft tech issues, non optimum levels resulting in increased burn and several diversions all of which where made far more comfortable by not planning to arrive with 30 minutes plus 5%.

14 diversions avoided in the last 12 months by carrying discressionary fuel of which 11 would of been overnights with accomadation for several hundred people plus the loss of an aircraft from a network for a minimum of 14-16 hours.

Runway behind, altitude above and fuel in the bowser...maybe you havnt heard that one...

 

 

 

[skelsey 765]

Daryl,

I think perhaps you are misunderstanding what Ian is saying. 

He is not talking about turning up with 30 minutes plus 5%. He's talking about turning up with 30 minutes, plus the alternate fuel, plus enough fuel to cover everything that 95% of previous flights burnt on top of the rest of the plan, plus any extra fuel on top of that. 

If 95% of previous flights used an extra 10 tonnes, that is what the contingency fuel will be planned at - not 5%. And if you want more on top of that, as Ian suggests, more is taken (I believe the plans also show the figure for 99% of previous flights as well).

Using actual fuel usage data to compute the flight plan is surely a better system than the company just giving you a standard 5%, no? In fact, it makes it entirely possible that Ian could be turning up somewhere with more fuel on board than you, despite the fact that he's only taken what's on the plan whereas you have come up with an 'extra' figure on your own.

Then again, I'm just a journalist, so what do I know... I'm sure there's an orphanage to be narrowly avoided somewhere in this story .

[fluffyflops 1,858]

2 hours ago, DEHowie said:

I guess the difference is you assume that turning up with 30 minutes gas is ok because 95% of the time it all works out? What about the other 5% of the time?

You missed the point of my post entirely as it was regarding turning up with 12 tonne of fuel...not 12 tonne plus an alternate plus contingency. So maybe tiger you should read my post again then reasses what your 12 tonne minus an alternate plus contingency equals...

I find it hard to believe in an industry where we plan for the worst case your happy to assume everything will be fine when things start to go wrong.

You assume airlines all carry alternates which in many countries they do not nor is there a requirement. So you do turn up with your 30 minutes plus whats left of your 5% or you have been planned to an alternate less than 5 minutes flying time away which would very easily be affected by unforcast conditions just as easily as your destination.

Anchorage and Elmendorf immediately to mind.

I think the hyd pump cooling has been covered nicely...thanks.

Feel free to be comfortable turning up to an airport with 30 minutes plus 5 percent of your last critical etp so about another 7-12 minutes because you know you never get unforcast weather, you never get un unplanned runway closures, you never get unforcast weather, you never have to go around and you always get your optimum flight levels oh and apparantly you never hold and your aeroplane will never break...nice how did you organize that? 

Meanwhile in the real world i have had numerous unforcast weather events, runways close, alternates go down with weather, aircraft tech issues, non optimum levels resulting in increased burn and several diversions all of which where made far more comfortable by not planning to arrive with 30 minutes plus 5%.

14 diversions avoided in the last 12 months by carrying discressionary fuel of which 11 would of been overnights with accomadation for several hundred people plus the loss of an aircraft from a network for a minimum of 14-16 hours.

Runway behind, altitude above and fuel in the bowser...maybe you havnt heard that one...

 

 

 

Trust me, this guy knows his stuff.   A pilot who knows his stuff when it comes to planning.. and also knows about commercial and fair weather alternates, you cant just divert from JFK and go to Newark just like that.

I also dont know any airline that will dispatch flights with only international reserves of 5 percent.  The CAA when they audited you here in the UK would revoke your AOC very quickly.

heres Virgins Alternates for JFK for example.. its a long way to Philly when youve only got 10 tonnes on !!!

 

[iwebber 207]

2 hours ago, DEHowie said:

I guess the difference is you assume that turning up with 30 minutes gas is ok because 95% of the time it all works out? What about the other 5% of the time?

Nope, never said that, I'm afraid you're going to have to read all the words I wrote, you can't just ignore a few, change the order of some or add some extras in, are you sure you're not a journalist?

2 hours ago, DEHowie said:

You missed the point of my post entirely as it was regarding turning up with 12 tonne of fuel...not 12 tonne plus an alternate plus contingency. So maybe tiger you should read my post again then reasses what your 12 tonne minus an alternate plus contingency equals...

The 12 tonnes I mentioned equates to 30 minutes reserve, contingency to cover 95% of extra fuel burnt by other flights in the past, a go around, SID, enroute, STAR and approach to a diversion airfield. To be fair, if I realised this was going to upset so many people I would have looked up some JFK contingency's which are probably generally more than 5 or 10 minutes so this would have all added up to a bit more than 12 tonnes.

2 hours ago, DEHowie said:

I find it hard to believe in an industry where we plan for the worst case your happy to assume everything will be fine when things start to go wrong.

You assume airlines all carry alternates which in many countries they do not nor is there a requirement. So you do turn up with your 30 minutes plus whats left of your 5% or you have been planned to an alternate less than 5 minutes flying time away which would very easily be affected by unforcast conditions just as easily as your destination.

We don't plan for the worst case and you're naive if you think we do, does your fuel policy include an allowance for engine out, stuck flaps, wheels part down, cargo door open, unpressurised diversion in icing and turbulence to an unknown distant diversion airfield, for just in case it happens? Of course not, we plan for realistically likely emergency's. When things outside of this occur we rely on pilot's airmanship. Don't get me wrong, that doesn't mean we ignore them but we rarely carry extra fuel for just in case the wheels don't come down (of course, if the aircraft has a history of it then I most certainly would).

I haven't assumed anything, I told you the sort of figure that we usually arrive with (12 tonnes). I don't understand the rest of that paragraph.

2 hours ago, DEHowie said:

Feel free to be comfortable turning up to an airport with 30 minutes plus 5 percent of your last critical etp so about another 7-12 minutes because you know you never get unforcast weather, you never get un unplanned runway closures, you never get unforcast weather, you never have to go around and you always get your optimum flight levels oh and apparantly you never hold and your aeroplane will never break...nice how did you organize that?

No, I wouldn't be, that's why we take more... (read all the words Darren, all the words)

2 hours ago, DEHowie said:

Meanwhile in the real world i have had numerous unforcast weather events, runways close, alternates go down with weather, aircraft tech issues, non optimum levels resulting in increased burn and several diversions all of which where made far more comfortable by not planning to arrive with 30 minutes plus 5%.

Yep, me too and given that we don't plan to arrive with 30 mins plus 5% (where did 5% come from??? - all the words Darren, all the words) I felt really quite comfortable. We have often taken extra fuel to cover any perceived delays it but do you know what, the number of times I've burnt more than the 95% contingency they originally gave us, ooo, I don't know, probably about 5% of the time.

2 hours ago, DEHowie said:

Runway behind, altitude above and fuel in the bowser...maybe you havnt heard that one...

I have, but we don't plan or operate our aircraft on banal clichés, we use facts, data and experience.

I really didn't think I was saying anything outrageous and I don't know why this has upset so many people, I appreciate I'm generalising somewhat but I still don't understand what's wrong with arriving at your destination (on a "normal" day) with 30 mins reserves, diversion and contingency to cover you for 95% of the time? If the day isn't "normal" then you add some more as appropriate. It doesn't really matter what it all adds up to, that's aircraft specific (but to bring this back on topic, in the jumbo it's about 12 tonnes).

Hope this clears it up, I suspect Simon said it better than me (but then he's a self confessed journalist )

Ian

P.S. Great photo's Darren, than Everts DC6 looks amazing.