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MC/Dx

Hi, Mike -

I flew the LAX-OGG route today, compensating as best I could for the fact that it's already got a 50kt CP built in (as mentioned earlier), and I noticed something else a bit troublesome: the release gives a ZFW of 184168, while specifying a Flight Profile of DINTY/F360.

My understanding (from Jeff) is that our 75Ws have the RB 211-535-C engine rather than the RB 211-535-E4 of our "mainland", non-wingletted aircraft. To make PHOG from DINTY, the aircraft should have about 45,000 lbs of fuel remaining, giving a total weight at that fix of about about 229K and change. I note that the specified profile is above the -E4-engined 752's optimum cruise level by over 1000 feet; I do not have the FPPM for the -C-engined aircraft, but it would apparently be even worse. I attempted to massage my .cfg and .air files for my 75W to approximate the performance of the indicated aircraft more closely (I don't want it climbing out like a U-2 after all!), but at a ZFW of 167.4, getting up to FL360 from DINTY was quite a bit of work.

And another concern: what are the (lateral) limits of RVSM airspace? DINTY should be (barely) observable by mainland radar, so may be RVSM, but what's the procedure for the next couple thousand miles (until within radar range of Hawaii)? (I am assuming that RVSM presupposes radar coverage, but I may be more logical than the average Federal Aviation Administration functionary in that regard...).

Please advise...

I flew a couple of them and it's worked out pretty well, I found a website that gives winds aloft,
so a little extra prep time, and I'm ready to go....Looking forward to when it's all in place, plus looking forward to a couple new airports to fly to..... Thanks Mike for all your work

Dave,

I don't really have any provisions for adjusting performance with the FOC program. What I can do is change the enroute cruise altitude to FL340 if you think that would work out a little better.

As far as RVSM out over the water, LA Center will run 1,000 foot seperation. Often times I see my first four PHX/Hawaii trips cleared at 340/350/360/370 running across the D-Track.

Mike

Hi, Mike -

It seems I misspoke: I do have a "short form" FPPM for the R-R RB211-535-C powered 752. For an aircraft weight of 229,000 lbs the Optimum Cruise Altitude is given as 33,400, while the Cruise Limit Altitude for that weight is 37,400 at ISA+10 and colder. I evidently need to readjust my .air file just a bit to improve the bird's capabilities (when I flew the route, conditions were ISA +7).

FL360 is thus rather uneconomical until about DIALO, where the fuel burn brings the Optimum Altitude in line with the flight profile. FL340 may be a better choice. It seems to me planning a step climb is not warranted on this route. Time for me to tweak the .air file, I guess.

Thanks for all the work you do for us. The route worked really well except for the altitude question noted. Thanks also for the answer regarding RVSM for this route. I think someone needs to produce a primer entitled, "RVSM For Dummies".

Howdy Dave,

During training for the North Atlantic Operation they taught us that it works a little better in terms of overall fuel use to plan slightly higher than what would initially be optimum and then let the optimum altitude "drift up" to meet the airplane. If you don't think our performance will be good enough I can certainly alter the plan for FL340

Mike

Hi, Mike -

No need, I can see the logic. With jets in general, it's usually better to be too high than too low. I will fix my .air file to better correlate with the book performance.

This is a bit of a tough one as I analyse it, as near the end of the cruise phase, where the weight should be down to about 200,000 lbs, the Optimum Altitude is only 36,200. There is also the headwind consideration(ususlly higher at higher altitude) while the GS will decrease with increasing altitude due to lower OATs, all to be balanced against fuel consumption which typically decreases with higher altitude... Gah! No wonder you guys get the big bucks!

It is easier for me to correct my .air file.

Hi, Mike -

I did re-check my thrust factors in my .air file, and found quite a few of them to be about 3 percent low. They have been corrected, and while getting direct to FL360 at the release ZFW is somewhat of a strain, it is at least achievable, 3 percent may not sound like much, but it does correspond to over 1000 pounds of thrust per side. If anticipating a significant headwind (over 50 kts), it may be necessary to delay the final climb segment past DINTY, but that's about it.

In sum, other than editing the FP for a zero-wind default (still needs to be done), it works fine. The airplane really doesn't like the profile (or perhaps I'm just too used to the 757 loafing along), but it can do it. I flew in ISA +10 (at altitude), and it spent a lot of time at CLB/CON thrust limit, showing an EPR of 1.82 even some time after TOC, and when I finally observed a reduction, it was only to an EPR of about 1.62.

Dave,

Thanks for all the performance research on this. It sounds like FL340 is going to be a more realistic/achievable flight level.

MC

Thank you, Mike! I really hope my contributions have been useful, and that I have not merely "muddied the waters".

I understand that the FAA has conducted some interesting tests of late, in cooperation (I believe) with UAL. I don't know whether scheduled commercial flights were involved, but some SFO-HNL (and return) runs were conducted with a profile considerably different than that currently used: rather than CLB/CON thrust up to a fixed FL, reportedly these tests involved setting up a cruise climb condition to optimum altitude, and allowing the a/c to drift up as fuel burn permitted. Also, rather than the somewhat Stuka-esque power rollbacks and plummetting descent rates past TOD, these tests called for rather more gradual letdowns. It would seem that "Keep 'em High" may be on it's way out.

While I don't recall the results specifically, I believe they achieved some not-inconsiderable savings in terms of burn over the route. I am intrigued enough to try this sort of thing myself just for grins 'n giggles, and will advise of my results.

I had not heard about any of those tests between SFO-HNL.

However, back in Jan/Feb of this year somebody at the FAA got bored and dreamed up this idea that they'd use "Flex Tracks" between the LAX/SFO area to the islands in addition to the fixed airways in place now. The flex tracks would be active by NOTAM only, and would be precoordinated with the military to avoid any hot warning areas off the coast. Apparently the thought was to emulate the dynamic track structure over the North Atlantic.

In the six weeks this was in place it was only used twice, and I heard UAL presented the FAA with such a compelling argument against using it (mostly due to the additional route miles and associated fuel costs) that they scrapped the whole program.

Progress goes *boink* (Calvin and Hobbes)

Mike

Hi, Mike -

Well, possibly I copied the information wrong: my efforts to duplicate those results were resounding failures. I tried the supposed profile twice, (near as I could figure within the limitations of FS9) getting inferior results each time.

The profile I flew involved a VNAV path climb until 10,000' (to clear the G/A traffic), a second-stage climb with V/S at 1500 to FL180, a third stage climb at 1000 fpm to F/L280, a fourth stage climb at 500 fpm to FL330, and a final stage at 200 fpm to Optimum plus 500'. As fuel burned off and the Optimum Altitude increased, I adjusted with 100 fpm adjustments to maintain Optimum plus 500'.

The summary of results is that the experimental profile took 10 minutes longer to touchdown, and burned a few hundred more pounds of fuel, while requiring a considerably greater workload (altitude adjustments at about every 15 minutes) than the standard flight at FL360.

Ah, well..."boink", indeed!

Hi, Mike -

Well, I tried a couple more experiments with MCA 2112, this time with default WX (which in FS9, is reasonably close to ISA Standard, although there is a 25-kt westerly wind aloft...)

The runs were timed from brakes off at LAX to full stop at OGG, the intent being to eliminate the vagaries of taxying. The first run was made at the old altitude specified in the release, FL360. The enroute time was 5:15, with a burn of 43,957. Flying VNAV and our standard 300/0.78 schedule, I made DINTY at FL354, DUETS at FL357 and finally got to FL360 at DADIE -280NM. (The PSS has an Altitude Capture that works more like an Altitude Snatch: at FL359 it abruptly went to 500 fpm climb while the airspeed decayed, resulting in attaining FL360 at only M=0.775. I have observed this characteristic previously on other flights.)

The EPR remained at the final CLB setting (1.80) for a bit as the aircraft slowly accellerated after TOC: M=0.780 was regained at DADIE -191NM, and M=0.790 was attained at DADIE -139NM. The programmed ECON CRZ was reached (M=0.798) at DADIE -107NM. Total time to accellerate was 0:26(!).

A second run was made similar to the first, but with the cruise altitude at FL340. The total time for this flight was 5:11, with a burn of 43,146. No accelleration problems at this flight level. I wish to try a couple of step climb alternatives, and will report on them when done...

Hi, Mike -

It occurred to me in trying step climb profiles that one of the problems with the POSKY/PSS merge I'm using, is that the numbers on the VNAV CRZ page in the FMC are based on the R-R RB211-535-E4B engine the PSS is modeled on. I tried two profiles involving step climbs, one following the prompt from the PSS FMC, and one involving flying the step climb according to the book.

The difference is quite noticeable: While the book for the -535-C engined 757 gives the Optimum Altitude Weight for FL350 at 212,000 lbs (with a ZFW of 184,168, thats a Remaining Fuel Load of 27,832), the FMC calls for a climb to FL360 with 32,500 Remaining Fuel, an GW of 216,668, a difference of 4668 lbs!).

(I should note for the non-technical people that, as I understand the SOPs, a step climb is typically initiated when Optimum Altitude is 1000 feet below your intended next cruise FL, repeating if necessary and able, although this does vary...)

The step climbs were in fact modified from both the FMC prompts and the book figures, to initiate the start of climb at a waypoint. This was done to simulate compliance with a VATSIM flight plan.

In the case of the test flown using the FMC prompts, the step climb (FL340 to FL360) was initiated 90 NM early, at DADIE. There was, again a bit of a waiting period while the a/c worked back up to cruise speed after the climb. The elapsed time for this test was 05:12, with a burn of 43,421.

For the test flown "by the book", the step climb didn't take place until DIALO, in this case delaying the climb by 72 NM, again for VATSIM planning purposes. This test had an elapsed time of 05:11, with a burn of 43,504.

I am frankly at a loss to explain those numbers. In any event, it does indeed seem that FL340 without step climbs is overall the best solution for MCA2112. Step climbs can be a somwhat bothersome prospect for planning, and ATC vagaries could trash all the careful fuel planning. The "drift-up" profile could probably be improved somewhat, but could be prohibitive from the ATC point of view, perhaps requiring the filing of a block of altitudes (good luck with that!) and being rather demanding of the flight crew.