Posts about: "LHR-BGI Route" [Posts: 10 Pages: 1]

shanewhite

Following the excellent explanation given by ChristiaanJ about the relationships between OAT, Mach number, TAS and IAS (which I have now copied and shall shamelessly pass off as my own work in future ) if you wish to see how these relationships work in practice you might look back at the photo posted at reply #66.

You will see that at FL600 the aircraft had a GS of 1,139 kts whilst flying at M2.00 and an IAS of 429 kts.

We don\x92t know what the wind was, nor what the TAS or OAT were, but we can easily deduce that:

• If the OAT was standard at FL600, at -56.5\xb0C, then, as at that temperature M2.00 equates to 1,147 kts TAS, in order to have a GS of 1,139 kts, she must have been flying into an 8 kt headwind.

• If the wind at that altitude was calm, then her GS of 1,139 kts must have been the same as her TAS. For M2.00 to be 1,139 kts TAS, then the temperature at FL600 must have been 3\xb0C colder than standard, at -59.5\xb0C.

• If , as was typical on a LHR-BGI sector, the OAT at FL600 was 10\xb0C colder than standard, at -66.5\xb0C, then M2.00 would equate to 1,120 kts TAS, so to have a GS of 1,139 kts, she must have been flying in a 19 kt tailwind.

For obtaining Mach/TAS/Temp values quickly and easily, as well as other useful information on the atmosphere, this Standard Atmosphere Calculator website is extremely useful.

Best Regards

Bellerophon

Hi Steve, good question. You could not prime Alt ACQ directly from MAX CLIMB/MAX CRUISE, but I'm sure the guys would confirm that FL600 was nonetheless set in the AFCS altitude window. If you did come close to FL600, then you would get an altitude alert audio and visual warning anyway, but the crew would obviously know anyway. The guys will have to confirm this but I think that ALT HOLD would be selected at this point, and the autopilot would now constrain the altitude by varying pitch attitude. You would normally be flying in nice cold conditions for this to occur, hardly ever on the North Atlantic, but on the LHR-BGI sector it would occur as often as not. (As usual, apologies to my all flying pals if I'm talking rubbish again ).

Dude

spfoster
Hi again Steve. At FL600 your aircraft is going to be relatively light, and your autopilot is set to ALT HOLD mode. As the aircraft continues to burn fuel it will 'try' and climb, but the ALT HOLD mode will of course slightly reduce pitch attitude to keep prevent the aircraft from climbing. The autothrottle in MACH HOLD mode can keep us from straying from Mach 2, large positive temperature shears were to my knowledge almost unheard of, and so any speed reduction was exceedingly unlikely. We really need a pilot's input here to further clarify the realities of LHR-BGI supersonic cruise; that's the way the AFCS was designed to do things however.

Dude

M2Dude has it all correct here. It only really happened regularly on the LHR-BGI route (low temps at crz alt, and light weight as you've burnt most of the fuel).

In the MAX Cruise mode the aircraft would sniff about vertically, gently climbing and descending to hold M2 (following the temperature changes), but with an overall general climb.

Heading to BGI you were climbing into very cold air, commonly down to less than -70degs, I saw minus 80 on multiple occasions. (Which was all very good news from a fuel point of view). So the climb was more definite and the likelihood of a subsequent descent lower.

It was pretty easy to spot when the aircraft was definitely going to 'stick' at FL600, and to select Alt Hold, with the already armed AT (with Max Crz mode) engagd in Mach Hold. Very occasionally one may have to subsequently make a subsequent return to Max Crz mode if warmer air was encountered, but I don't recall doing this more than once.

If you had very cold air and a lighter than average load, one would find that the throttles (no 'thrust levers' on Concorde!) were quite a long way back at TOD, maybe 10-14 degrees throttle angle. It was worth noticing this early - the decel/descent was initiated by reducing the throttles to 18degrees, normally this would be from full forward so it can be seen that reducing them by 4 or 5 degrees rather than the usual 18 could result in a disappointing rate of decel. At nearly 20NM a minute this could really screw your descent plan! (I think the record-holders went past BGI still just the wrong side of M1......)

I used to enjoy the last few minutes of the flight at FL600 - before the space station was manned and post-MIR there was a fair chance that at that moment we were the human beings furthest from the surface of the planet. In shirtsleeves, with a cup of tea (or something more palatable if one was in one of the comfy seats).

Nick Thomas


... on shorter charter flights was there a mininium ammount of fuel that had to be loaded just to always have enough fuel for CofG movement...

Yes, 35,000 kgs, at take-off, for a short supersonic flight. This would allow sufficient fuel to be transferred rearwards in order to achieve a CG approaching 59%.

If the flight was to remain subsonic, the fuel figure dropped to 25,000 kgs, as the required CG for subsonic cruise was 55% not 59%.

Both these figures were at take-off, so the estimated taxy fuel had to be added to these figures in order to arrive at the minimum fuel figure required to be loaded.


...was it possible to be in a position where trip fuel, fuel to an alternate etc was less than the fuel required for CofG movement after take off?...

No, at least it should not have been!

However, a situation was sometimes reached in flight, generally only towards the end of the planned supercruise portion of a LHR-BGI sector, where, with the aircraft at M2.00 and FL600, it was no longer possible to maintain a CG of 59%, as the "ballast" fuel, which had been transferred aft into tank 11, was now required forward again as "fuel" fuel, to top up other tanks which had reached their minimum permitted levels.

In this case, once the forward transfer of fuel had begun, the CG would also be slowly moving FWD, and one would be compelled to commence the decel and descent earlier than desired, something EXWOK touched on here much earlier in this thread.

Best Regards

Bellerophon

For spfoster:

You've pretty much worked HLI out. No particular special requirements, it was normally associated with 54% CG departures, since that was the norm with high fuel loads.

Contacts were bridged which allowed some of the tanks to operate at a higher level before shut-off. Sounds simple, doesn't it? But it was a pain in the a***.

The tanks were first filled to normal level (this got tank 11 filled) then a metered amount was uplifted with the bridges in place to those tanks with HLI (M2dude will remind me which they were.....I'm guessing 5,6,7,8 and maybe 9&10?????). It could take ages.

It was invariably followed by a taxy with a Pre Take Off Burn Off to get the CG to its correct position, so you now had the problem that you had to burn enough fuel from tanks 1-4 to allow them to be topped up by tanks 5 & 7 to the extent that 5 & 7 could accept fuel from tank 11 to bring the CG fwd to 54%. Because they were so full it could take ages to get 5 & 7 to accept fuel and then any bump or turn would shut them off. So overall you've filled the tanks, presumably because you need the fuel, but because you've done this you have to burn loads of fuel taxying while you get the CG sorted out.

As you guess, it was mainly a LHR-BGI thing, or a JFK with weather problems, and more often than not you gained very little.

hissinsid;

The answer is that they were remarkably similar in handling, I guess this is a function of the flight control system. Certainly the 747-100s and 200s I flew before Conc had a definite change of 'feel' from hull to hull. (The 777s don't).

They all had certain other 'foibles', although none were of any note operationally. I believe that AF's habit of generating ADS master warnings at M1 has been prevously covered, as has AG's 'French' DC system. There were certainly some hulls you'd rather have than others on the LHR-BGI sector, although I think I flew them all there at some point or another.

As for Filton - it's always sad to see an airfield close, but especially so when there's so much history attached. It would be great to see the runway remain active, but the costs are pretty steep and the value of the land rather high. I wish all thise involved the very best of luck and hope you succeed in at least turning the hangar into something which recognises its own history and gives it a real purpose for the future.

fizz57


As well as carrying sufficient fuel to arrive at BGI with standard fuel reserves remaining, there was also a requirement that sufficient fuel be carried to ensure that, following an engine shut-down at any stage in the flight, Concorde could divert, on three engines, to a suitable diversion airfield, and still arrive there with standard fuel reserves remaining.

It was this requirement - the three-engined diversion requirement - that often required more fuel to be loaded - above the basic LHR-BGI flight plan fuel figure - often bringing the total fuel required up to or over the full tanks figure and so became the limiting factor on this route.

Perhaps the main difference between Concorde and most subsonic aircraft, following an engine shutdown in cruise, was that Concorde would suffer a much greater loss in range. From four-engined supersonic flight to optimum three-engined subsonic cruise the loss in range would have been in the order of 30-35%.

This was mainly because Concorde, following an engine shut-down in cruise, would have to decelerate and descend, and thus leave a very efficient flight regime, at M2.0 and 55,000-60,000ft, with relatively low drag, low winds and very cold outside air temperatures, for a much less efficient regime, at M0.95, at around 30,000ft, in a higher drag subsonic cruise with warmer outside air temperatures and much stronger, probably adverse, winds.

The forecast weather at the principal en-route diversion airfields of Santa Maria, Lajes, Bermuda and Antigua, along with the calculated wind components at subsonic cruise levels to these airfields, were all taken into account at the flight planning stage, with the forecast subsonic cruise wind component to Antigua generally being the most critical factor.

If the weather conditions at and en-route to these diversion airfields were favourable, flight planning was straightforward. If the weather conditions were unfavourable, flight planning got more difficult, but the necessary fuel was always carried, passenger numbers limited or a re-fuelling stop planned.


No, not really.

LHR-BGI was certainly the most demanding route on Concorde, and required careful planning, good tactical awareness and diligent in-flight monitoring, however the flight planning procedures and tactical decision making processes were standard and would have been very familiar to any ETOPS rated pilot.

With one exception.

Concorde would still have got you to a diversion airfield following a second engine failure!

Best Regards

Bellerophon

Time for descent may well have been a certification requirement for max FL - others will know better than I…

I don't believe the ramp schedules were designed to operate far above FL600, I vaguely recall that FL635 was the highest reached during testing but, again, others will know better. A typical LHR-JFK or JFK-LHR would get to between 570 and 590 depending on weight and OAT, LHR-BGI almost invariably ended up level at FL600 due to lower weight and much lower outside temps.

As for reverse inflight, off the top of my head the limits were; Max FL300, speed 250-380kts, max use 4 mins. It didn't make a vast difference to RoD, although it was noticeable.

Inflight rvs was limited to engs 2 and 3 but to enable sufficient air to deploy the reversers, engs 1 and 4 spooled up slightly (in fwd thrust) to help deployment. While this is going on the primary nozzles open fully (for the same reason) but after reverse position is reached, the 2 and 3 primary nozzles have to close to 15% otherwise you get a 'CON' light which means reverse has to be cancelled on that engine (this was not a rare event).

Common sense and airmanship also dictated that you had an escape plan if one or both the engines didn't get the secondary nozzles out of reverse, so you didn't want to do this if fuel was tight.

All-in-all it was far better to make sure you didn't need reverse inflight!

Did LHR-BGI always tech stop in SNN ?