Above or Below OPTIMUM ?

[Driver170 42]

Ok NGX pilots

 

Your doing a flight from EGGP to LSGG and the FMS CRZ page is showing OPT 402 / MAX 410. Your OFP has a planned cuising FL of 410 because you can't use FL400 (OPT) because its a EVEN FL.

 

France RVSM use SOUTH bound flights ODD FLs and NORTH bound EVEN. Unlike the standard ICAO East/West rule for some countrys in Europe.

 

You're the captain and need to decide - would you cruise at FL410 MAX Certified alt / MAX ALT or do you cruise at FL390 - 1000ft lower than OPT or 1000ft higher than OPT FL410.

[kevinh 409]

If you were cruising at FL390 and the optimum was FL402, VNAV would recommend you to step climb to FL410. So that's the level you should ideally fly at.

[Driver170 42]

Yeh but flying above or below have there advantages and disadvantages!

[Guest]

Generically speaking we stick to the fixed speed/cost index and flight level shown on the flight plan. We're instructed to do the following regarding FMC OPT Altitude

 

- When the flight plan cruise altitude is LOWER than the FMC OPT Altitude we fly the flight plan cruise altitude

 

- When the flight plan cruise altitude is HIGHER than the FMC OPT Altitude we fly the FMC OPT Altitude.

 

You can fly anything up to the FMC MAX ALT but anything within 300ft in reality leave very little margin. The fuel savings on the sector quoted would be negligible anyway so you can just stick at FL390! You can actually, in certain instances in Europe, fly non-standard flight levels so you could ask for FL400.

 

You can do flights where you can be filed in the flight plan at something like FL260 for quite some duration and the OPT is FL410.

[Driver170 42]

Thats great sam. Either way going above or below your going to burn more fuel and depending on winds aloft. Is it true flying above OPT you have an increase of AOA which then increases induced drag and burns more fuel and you'll fly alot slower? And going below your AOA will decrease giving more thrust more parasite drag = more fuel burn but shorter trip time.

 

My rule is 1000ft below MAX ALT in rough air and 800ft in smooth air

[pcubine 143]

Ok NGX pilots

 

Vernon

How do you get that high in Europe? Low payloads? You know planes are usually packed in the U.S. On a 5 1/2 hour flight in the U.S., I have never seen higher than FL380. Maybe 3-10 empty seats with 8-8500 lbs . of cargo and baggage and 35 to 40000 lbs. of fuel.

[Copper. 78]

There are people that would consider those circumstances well before you leave the ground for you. It might also be a regulation for them to do so before you're able to fly your mission.

 

After consideration, they'll come up with the best "PLAN" based on historical data and operational experience, then they'll publish the best "PLAN" on - you guessed it - the "flight plan". Alterations can be made to the "PLAN" inflight to better suit the conditions you find yourself in (weather, traffic etc).

 

In sim world, I'd just fly one or the other, and keep doing that until I've built enough experience (by filling in the Nav Log of the flight plan), then compare all that data to satistically come up with the best course of action.

[ckyliu 1,749]

How do you get that high in Europe? Low payloads? You know planes are usually packed in the U.S. On a 5 1/2 hour flight in the U.S., I have never seen higher than FL380. Maybe 3-10 empty seats with 8-8500 lbs . of cargo and baggage and 35 to 40000 lbs. of fuel.

The answer is in your question, "a 5 1/2 hour flight" is not typical for 737s flying within Europe. An average 737 sector on a European airline would be 2.5 hours. Load factors can be often be 95%+ on LCCs, but there's little baggage in the hold because most carriers charge extra for that.

 

The OP mentioned Liverpool to Geneva, which is only 1h 50m scheduled flight time on easyJet A320.

 

Before everyone jumps on me and starts listing examples of much longer European 737 flights (because some people at Avsim like to show some sort of smug superiority), YES they exist but they are less common as a proportion (there's not many flights like Helsinki to Madrid, which is 4.5 hours and crosses from one side of the EU to the other). The longer 737 legs tend to be charter package holiday operators flying to Greece, Cyprus and the Canary Islands.

[Driver170 42]

 Guys check this out. surely no airline will have you at FL380 and then des to FL370 and back up to FL380. Anyone confirm this can happen?

(FPL-RYR1195-IN -B738/M-SDGIRWY/SB1 -LPMA1230 -N0447F380 SNT DCT OBESA DCT PETEK DCT BERUX/M077F370 T213 TAMEL DCT EVBAK DCT GAPLI/N0437F370 UN21 MERLY UL180 ASRAX/N0446F380 UT7 NITON UN864 MONTY -EGGP0334 EGNO -PBN/ A1B1C1D1S2 NAV/RNVD1E2A1 COM/TCAS DOF/151013 REG/RYR EET/LECM0133 EGGX0154 EGTT0245 RVR/200 OPR/ VRYREU -E/0426

--------------------------------------------------------------------------------
AWY      WAYPOINT   MT    ALT MSA FREQ    TAS  LEG  FUEL REM / USED   LEG   ACC
-FIR     NAME                 ISA WND/SPD  GS  REM  POSITION          ETO / ATO
--------------------------------------------------------------------------------
         LPMA/05          191 085                       10.4 /   0.1            
         MADEIRA                              1438  N3241.4 W01647.0 ...../.....

SNT6N    PST       049   *CLB 085 338.0         31       9.5 /   1.0   08  00.08
         PORTO SANTO          P10             1406  N3304.1 W01621.5 ...../.....

SNT6N    SNT       022   *CLB 030 114.90         1       9.5 /   1.1   00  00.08
         PORTO SANTO          P09             1405  N3305.4 W01621.0 ...../.....

         *TOC      031  FL380 030         447   94       8.6 /   2.0   13  00.21
                              P01 303/035 444 1311  N3430.6 W01532.2 ...../.....

DCT      OBESA     031  FL380 010         445  144       7.8 /   2.7   20  00.41
                              P03 304/017 443 1167  N3639.4 W01414.8 ...../.....

DCT      PETEK     020  FL380 010         444  377       5.8 /   4.7   52  01.33
-LECM                         P00 016/027 417  790  N4240.7 W01200.0 ...../.....

DCT      BERUX     021   *DES 010              146       5.1 /   5.5   21  01.54
-EGGX                         M02              644  N4500.0 W01100.0 ...../.....

T213     TAMEL     009  FL370 010         440  225       3.9 /   6.7   33  02.27
                              M01 336/039 406  419  N4843.7 W01029.8 ...../.....

DCT      EVBAK     055  FL370 010         435   26       3.7 /   6.8   04  02.31
                              M01 354/050 421  394  N4900.0 W01000.0 ...../.....

DCT      GAPLI     056  FL370 010         437   99       3.2 /   7.3   14  02.45
-EGTT                         M01 352/051 410  295  N5000.0 W00800.0 ...../.....

UN21     MERLY     058  FL370 030         438  140       2.5 /   8.1   21  03.06
                              P00 353/059 408  156  N5120.0 W00500.0 ...../.....

UL180    ASRAX     070   *CLB 030               29       2.3 /   8.2   04  03.10
                              P01              126  N5131.3 W00416.7 ...../.....

         *TOD      035  FL380 042         444   21       2.2 /   8.3   03  03.13
                              M00 353/057 398  106  N5148.7 W00358.9 ...../.....

UT7      IDOVO     035   *DES 042               29       2.2 /   8.4   04  03.17
                              P02               76  N5213.4 W00333.1 ...../.....

UT7      NITON     036   *DES 042               24       2.2 /   8.4   05  03.22
                              P02               52  N5233.2 W00312.0 ...../.....

UN864    MONTY     005   *DES 042               20       2.1 /   8.4   04  03.26
                              P02               32  N5253.6 W00310.4 ...../.....

KEGU1D   D186X     005   *DES 042                6       2.1 /   8.4   01  03.27
         WAL186024            P01               26  N5259.6 W00310.0 ...../.....

KEGU1D   KEGUN     005   *DES 047               12       2.1 /   8.5   03  03.30
                              M04               14  N5311.6 W00309.0 ...../.....

KEGU1D   EGGP/09   053     81 047               14       2.0 /   8.6   04  03.34
         LIVERPOOL                                  N5320.0 W00252.0 ...../.....

[scandinavian13 5,192]

 Guys check this out. surely no airline will have you at FL380 and then des to FL370 and back up to FL380. Anyone confirm this can happen?

(FPL-RYR1195-IN -B738/M-SDGIRWY/SB1 -LPMA1230 -N0447F380 SNT DCT OBESA DCT PETEK DCT BERUX/M077F370 T213 TAMEL DCT EVBAK DCT GAPLI/N0437F370 UN21 MERLY UL180 ASRAX/N0446F380 UT7 NITON UN864 MONTY -EGGP0334 EGNO -PBN/ A1B1C1D1S2 NAV/RNVD1E2A1 COM/TCAS DOF/151013 REG/RYR EET/LECM0133 EGGX0154 EGTT0245 RVR/200 OPR/ VRYREU -E/0426

 

Not sure. An airline might.

 

What you're seeing here is likely more to do with the MAA on an airway segment. They'd either profile it (descend for the segment), or just plan for the next available lower level that meets the lowest MAA on the route. To give a nod to greyviation, it's also worth noting that an operator may get a Letter of Agreement (LOA) from the control facility or Administration to waive that MAA.

[Driver170 42]

Its quite odd not sure what to do here. I would use the FL380 EVEN FL north bound in LISBOA FIR. And then step climb to FL390 ODD FL once in EGXX FIR instead of DES to FL370

[Guest]

Guys check this out. surely no airline will have you at FL380 and then des to FL370 and back up to FL380. Anyone confirm this can happen?

Quite common to see CLB and DES during different phases of a flight within European airspace. Flight plans aren't however followed religiously regarding planned FL. In this instance you'd most likely maintain FL380 traffic permitting. It's quite common to see stepped CLB/DES into different destinations.

 

For example, coming back to the UK from the South you might be filed to be level at a certain point which would usually leave you way below your FMC OPT cruise level by the time you descend to comply with the restriction. The actual restriction by the time you get there might be a different FL or not there at all!

 

Also first wave departures first thing in the morning in Europe usually see all the operators departing at once heading to the same country and/or destination. It's quite to common to not even get anywhere near your planned FL, that's why we carry contingency fuel.

 

You might also decide 10 minutes before departure to put on another 1200KG of fuel due to weather at destination. Flight plans OPT cruise level is based on the estimated passenger load and planned block fuel. Having shoved a load of extra gas on you're probably unlikely to make your initial cruise level because you're too heavy so you initially fly a lower cruise level. ATC are very flexible in Europe (except the Spanish!) and you can, traffic permitting, fly at requested levels as opposed to flight plans.

 

Hope I cleared some points up for you.

[Jetstream96 20]

Its quite odd not sure what to do here. I would use the FL380 EVEN FL north bound in LISBOA FIR. And then step climb to FL390 ODD FL once in EGXX FIR instead of DES to FL370

Suppose your OPT altitude is FL375. Then it'd be better to cruise at FL370 instead of FL390.

 

Btw I found the OPT ALT in the FMC is quite a bit different than the values from FCOM. It tends to be 1000 to 2000 ft higher than found in manual.

[Driver170 42]

Sam great stuff there what would be your call here in deciding what FL to use?

 

David thats interesting because i'm finding that too. I thought PMDG based it on the FCOM?

[Driver170 42]

David have you been looking at LRC in PD to get OPT altitude?