Pax/amateur question: reasons for extraordinary? transatlantic stop-over

[Failte]

A friend of mine told me she was flying from Las Vegas into Frankfurt, aircraft was a Boeing 767. She said that aircraft was climbing at very low rate, and take-off must have felt somewhat weird. Later crew told pax that they would have a stop-over in Iceland. The reason indicated was that due to high temperatures (about 45 degrees Celsius in Vegas) they could not fuel up to fullest extent necessary. Instead, from what I understand, the overall weight was 128 tons at take-off (maximum would have been around 180 tons?), lacking 4 more tons of fuel, which would have allowed them to go straight to Frankfurt. In Iceland, refuel time was very short, around 10 minutes, normal take-off etc. thereafter.

Is that a common procedure? Temperatures like that don’t seem to be unusual in Las Vegas, so why would an airline offer it a non-stop flight, if stop-over were predictable? And if you know you can’t make it to final destination anyway, wouldn’t you rather calculate fuel just to get to Iceland and fuel up again as if flight just started from threre again?

Thought I can get some input from you professionals, can anyone maybe comment on this? Thanks.

[WindSheer]

With the temp being around 45 degrees you are talking about losing quite a few tons of takeoff weight to meet the performance criteria....this could result in the fuel load being below the required (or very close to it), mandating a 'tech stop'.

so why would an airline offer it a non-stop flight, if stop-over were predictable?
Business is business...how many seats/bookings would they lose to the competitor if it was advertised as 'maybe direct'!!

And if you know you can’t make it to final destination anyway, wouldn’t you rather calculate fuel just to get to Iceland and fuel up again as if flight just started from threre again?

The cost of fuel is always known when refuelling, the crew would have known Iceland is more expensive than Vegas therefore forcing them to take off at max permissive weight to get as much 'cheap fuel' (yeah right!!) on as possible, requiring just a top up at Iceland. The other factors adding to this would be flight deck duty hours - the tech stop may have pushed them really close to maximum hours. Also, the aircraft may have already been pre-loaded with a large bulk of the fuel expected for a transatlantic flight before the pilots had calculated their ammended figure. Fuellers try and stay ahead of the game by 'pre loading' the majority of the expected fuel before the final figure is announced.

Hope this helps :ok:

[Piltdown Man]

Unless your friend was on the flight deck, they wouldn't be able to comment on the rate of cimb. And even if it was a lower rate of climb, there are many reasons as to why his could be advantageous. But going back to the basic question: You don't stop for refuelling for the hell of it. It is too expensive. Nor do you depart without sufficient fuel for the flight "intended" destination. Also don't forget that the chappies driving the plane may have planned to go Iceland in the first place. Finally, we don't know of the aircraft's status nor that of the airport of departures. Deficiencies in either (or both) could have reduced the aircraft's ability to lift all of the fuel required, exacerbated by the temperature. Sounds like a proper airline though.

PM

[Rainboe]

Payload may have been heavier than usual. En route winds may have been less favourable than usual extending flight time and making destination difficult at that take-off temperature. They may have set off with the hope of being able to re-plan fuel in-flight and perhaps make destination, but if they ended up even more unfavourable may have had to divert as planned anyway. Maybe they had some special defects restricting altitude they could fly at, hence efficiency, or limiting fuel load possible for a special take-off weight limitation. Take your pick.

[SNS3Guppy]

We often plan for direct flights based on a re-release over the Atlantic. Sometimes we end up going to Gander for fuel, often as not we are direct. We are able to plan for reduced fuel reserves using a "re-release point" where we must call the company and obtain a determination along with a dispatcher regarding our fuel state and ability to continue. Even though the flight is launched as direct, we're released within the company to an intermediate point. If we don't have the necessary fuel reserves to continue, we'll divert to a nearby planned airport; if we do have the necessary reserves we'll continue. This is all carefully planned in advance, and it's predicated on legal reserves, not just on the necessary fuel to make the trip.

Each flight is required to have a certain amount of reserve fuel based on the nature of the flight and flight conditions. The amount of required reserve fuel varies with where it is and what we're doing. We prefer not to carry more reserve fuel than necessary (within reason, obviously) because extra fuel and extra weight actually means we burn more fuel...the more extra fuel you carry, the more you end up burning, and in fact, the less fuel you really have...your reserve goes down.

The re-release allows us to use a reduced legal reserve fuel, but requires that upon arriving at the mid-point, or re-release point, we are able to recalculate our fuel and find that it still meets all the necessary requirements to continue to the destination. In effect, it's two different flights; one to that point in space, and one from there to the destination, with some very specific requirements that must be met. For the purposes of anyone watching the flight, it's one seamless trip beginning to end...unless we find that the fuel burn has been higher, the trip slower, the winds more adverse, the temperature unfavorable, etc.

Another way of looking at it is a plan to cover all eventualities. For the passenger end, the use of a re-release allows the cost to be streamlined by reducing the weight of the flight (less tankered fuel), and the costs for the ticket to be ultimately lowered. It's all part of the big picture, but safety is always first, and that diversion to Iceland is part of the cost of safety.

Accordingly, especially with the price of fuel today, the fuel planning must be very exact. Changes in the flight conditions are not always predictable, however. Higher than expected temperatures, winds different than forecast, etc, mean that the amount of reserve fuel we expect may not be there. We keep very close track of the planned fuel burn and the actual fuel burn as we progress along our intended flight track. If we find that the reserves are not adequate as we approach our re-release point, then we have no choice but to use the alternate. As others have said, we'd prefer not to use the alternate or re-release airport, because it takes extra time, creates delays, adds expense, and means we burn even more fuel when we climb back up to altitude again.

[Mark1234]

In simple terms (it does say pax/amateur question - I'm not being patronising); The hotter and higher you are, the thinner the air is. The thinner the air is, the faster you have to go to lift off as the wings have less to push on, and the less effective the engines are as they have less to push with (simplistic) - double whammy.

It sounds like in this case the runway length available to accelerate was the limiting factor - so you choose a (lighter) weight that will get airborne in what you have available, according to Mr Newton's third law, for a given amount of force (thrust), the lighter it is, the quicker it will accelerate (and the lighter it is, the easier it flies (double benefit).

Not I only pilot little stuff, but 4 tons of fuel doesn't seem like a lot in the grand scheme of a 128ton takeoff weight - It's probable that normally they're fine - a few degrees cooler, more favourable winds etc.

SNS3Guppy has explained the situation with fuel/fuel burn better than I ever could.

So, I would say yes, out of the ordinary, but not that extraordinary..

And for Piltdown Man - no hard numbers down the back, but relative rate of climb is quite evident, so long as there are some visual cues (like the ground disappearing); e.g. from london to sydney the departure from london is usually noticably more lethargic than the one from singapore (the second leg being much shorter). Fly much, even as pax, you get a feel for what's 'normal'..

[411A]

Seems to me that the operating crew had things well in hand...and safe.
Better than Qantas and MAS, for example, landing one of their B747-400's at LHR with 3 tons of fuel remaining, some years ago.
All those nice enroute airports available, yet they pressed on, regardless.
Not especially bright.

[pattern_is_full]

Failte: In addition to the physics of high, hot takeoffs already discussed, there are a lot of other variables that may have come into play in causing this particular flight to require the refueling stop on this particular day:

Winds aloft (Jet Stream) may have been unusually weak or have drifted N or S of the planned route of flight - removing the "help" of a 30-60 knot tailwind (50-100kph). On an 10-hour flight, that can make a big difference (300-600 miles) in whether you can get there in one fuel load or not.

Passenger loading: Maybe all the seats were full and everyone brought 20 extra Kg of luggage on this day, using up weight capacity that could be devoted to a few extra gallons of fuel on other days.

In other words, this flight may well have been non-stop 90% of the time - but on the 10% of days when all the factors lined up wrong, it requires a pit stop. Kind of hard to schedule a flight as "90% nonstop."

Also remember that just because the refueling took place in Iceland, that doesn't mean the plane only had fuel to reach Iceland. it may well have had fuel to reach London, Paris, Schipol or even Koln (regulations are strict about the difference between having enough fuel and having "almost" enough fuel) - but Iceland was likely a preferrable stopover due to lower traffic, faster in and out, fuel price, or whatever.

[EnzoC]

My guess is that this was a DE flight that took of from RWY 07 in Las Vegas.
Legally you have to limit your T/O weight so that you can still clear all obstacles in your takeoff flight path, with one engine failing during takeoff run (I'm not going deeper into the regulations at this point).
RWY 07 in LAS leads out over some obstacles into quite nasty terrain.
On hot days (above 40-something degC) your takeoff-weight due to the obstacle situation is limited to an amount, where you just can't take up enough fuel for going to FRA (the alternative to drop off pax and take more fuel instead is not really a good choice having only one flight a day).
Typically, there is a re-fueling somewhere before crossing the pond, due to crew-duty-time issues. Iceland seems a bit way off, but could be on that specific day due to weather/wind.
So: re-fueling on this flight might just happen on hot days in LAS
And: crew and dispatch did everything right, they were just limited by takeoff weight

[Failte]

For the avoidance of doubt I should mention that my friend felt absolutely safe and comfortable. She also added that the information screen in the cabin showed a clearly shorter “time to destination” right from the beginning (about 7 hours which obviously referred to Iceland), and Captain made the announcement half an hour after departure.

Personally I do appreciate (more detailed) announcements from the flight deck, but that’s maybe just me being curious (or call it enthusiastic).

Anyway, thanks a lot to all of you for taking the time and giving a really interesting insight into how many factors may have influenced that particular flight

[pattern_is_full]

"Iceland seems a bit way off, but could be on that specific day due to weather/wind."

Great circle routes are funny things - actually the KLAS-EDDF GC direct comes very close to Iceland - at least as close as it does to other major European cities, since it sort of drops down through the North Sea in Germany at the end.

[EnzoC]

"actually the KLAS-EDDF GC direct comes very close to Iceland "

If they flew close to GC that day then Iceland is an option ;-)

On the eastbound track system you will find more southernly routes that take advantage of the jet streams. Thus you save fuel by not flying the shortest distance.

[BEagle]

The poor accel/stop performance of the B767 at high AUW and OAT, particularly at significant pressure altitudes, is one reason why the KC-767A would have been such a markedly inferior military tanker compared to the infinitely more capable KC-45A!

A fact I was provided with by a senior Boeing chap some years ago - "That's where Airbus have the upper hand", he said.

Anyway, good to learn that at least there was no gambling on this Las Vegas occasion!

[mathy]

Care to offer figures from the B767 and A330 manuals? Someone of your unique experience, distinguished service and noted freedom from bias or controversial opinion floating unattributed hearsay sounds like rumour to me. Oh darn, this is a professional pilots rumour network. How's the A310 tanker and A400M coming along these days BEags?

Bless

[Admiral346]

The A400 was introduced at Sevilla / Spain yesterday and is scheduled to do it's maiden voyage in about 6 months.

How's that 787 flight testing going, sir? Just asking, while we're at it?

Nic

[glad rag]

Perhaps you might prefer to use the forums SEARCH function to find the answers you seek...........................:ok:

[mathy]

You'd have to ask someone from Boeing 787 wouldn't you? Maybe the Boeing chappie dear Beags threw into the mix as hearsay whilst referring to an "infinitely superior product". Which he is quite entitled to do on a rumour network. Just as he is entitled to omit any connection he has/had with another manufacturer. But thank you for your riposte nonetheless. Not a veritable hit sir, but close. I thought that the nom de plume would not be so easily unravelled. Cut and thrust, sir, with manners and no ill feeling. Just how it should be. Does anyone have any input by the way on the US tanker contract award procedures controversy? Preferably without rumour and preferably with interests declared.

[Pub User]

Temperatures like that don’t seem to be unusual in Las Vegas

According to this information:

Holiday Weather - Weather Averages for Las Vegas, USA (http://www.holiday-weather.com/las_vegas/averages/#avg_high_low)

they are indeed quite unusual.