737 NG Questions

[rocketfs 2]

My takeoff ref page does not show all this info. Is it only available in the -800/-900 version?

Takeoff Ref page: there are 2! (I didn't check if this is 800/900 only though.)so click next page and look bottom right.THR REDUCTIONCLB 1500 AGL.So the PMDG 738 is standard set to have thrust reduction at 1500' above ground level. The thrust reduction altitude is probably defined by the engine manufacturers specifications. It allows high power for takeoff but needs to be limited in time to prevent engine damage due to overheating and other factors.Some moderne 737 engines even have a bump function that allows even more power. Used for short field takeoffs (and maybe go around?).Bert Van Bulck

[NG_Aviator 39]

Hi GuysAnother question, this time about engine start switches!! After start, you position the engine start switches to CONT. Do you leave them in CONT all flight?Regards

[rocketfs 2]

Hi GuysAnother question, this time about engine start switches!! After start, you position the engine start switches to CONT. Do you leave them in CONT all flight?Regards

I thought this:Switch them OFF: after takeoff, after landing.Switch them ON: before takeoff, when flying in visible precipitation (rain, snow, hail,...), when anti-ice is activated, before landing (see landing checklist)But apparently since 2005 things changed and they stay on in flight.737 checklists old vs newBest Regards,Bert Van Bulck

[Spin737 102]

Engine start switches are off on the after takeoff check and are Cont with Gear Down/F15 on approach. They are not normally on the entire flight.If your plane has (is modeled with) auto-ignition (whatever that is. . . ) I guess you don't monkey with the switch. After start, it's OFF. Either way, the switch isn't on in flight unless you're in some icing/turbulence/emer descent/etc.

[fencer 16]

Takeoff Ref page: there are 2! (I didn't check if this is 800/900 only though.)so click next page and look bottom right.THR REDUCTIONCLB 1500 AGL.So the PMDG 738 is standard set to have thrust reduction at 1500' above ground level. The thrust reduction altitude is probably defined by the engine manufacturers specifications. It allows high power for takeoff but needs to be limited in time to prevent engine damage due to overheating and other factors.Some moderne 737 engines even have a bump function that allows even more power. Used for short field takeoffs (and maybe go around?).Bert Van Bulck

Bert,You'll notice the thrust reduction altitude is adjustable : you can modify it in page 2. But if I remember well what a rw pilot told me, ICAO regulations make it mandatory to maintain at least 75% of full thrust until the take-off phase is over - ie 1500 ft above the ground. You can have derated power but it must be avove 75% of full thrust. Then, whether you take off at full rated or derated power, you'll apply thrust reduction, so prevention of engine damage is not the main factor here. Could the rw pilots in this thread please confirm this?Bruno

[fencer 16]

Engine start switches are off on the after takeoff check and are Cont with Gear Down/F15 on approach. They are not normally on the entire flight.If your plane has (is modeled with) auto-ignition (whatever that is. . . ) I guess you don't monkey with the switch. After start, it's OFF. Either way, the switch isn't on in flight unless you're in some icing/turbulence/emer descent/etc.

Hi Matt, If I understand correctly, some NGs have "auto-ignition" and require no action of the switches for normal take-off/landing (action is required only in case of icing/turbulence/emer descent etc.) and others still require the pilots to manually turn them on/off before/after take off and landing (and therefore have the corresponding instuctions in the checklists).Is that correct?Thanks in advance,Bruno

[scandinavian13 5,192]

I won't comment on ICAO regs, because all I pay attention to is the FAA. I will clarify, however, that preventing damage is not the main factor. The main factor would be preventing excessive wear (the same goes for the APU restrictions on using bleed 1 min after start and 1 min before shut down). More stress results in higher wear. Damage is really only an issue when operating outside of the engine's designed parameters. Engineers design with a certain percent margin in place so that even going outside of the envelope won't immediately cause a failure, but it will eventually happen if pushed too far or too long. Damage from use (with no external causes: FOD, volcanic ash, etc) is rare unless the engine is outside its normal limits, so it's really wear that is the prime concern.

[Spin737 102]

Hi Matt, If I understand correctly, some NGs have "auto-ignition" and require no action of the switches for normal take-off/landing (action is required only in case of icing/turbulence/emer descent etc.) and others still require the pilots to manually turn them on/off before/after take off and landing (and therefore have the corresponding instuctions in the checklists).Is that correct?Thanks in advance,Bruno

I've never flown a 737 that had the auto-function, so I don't know. I would hope it would come automatically with engine-anti ice, but that would make things easy. Otherwise, what you say sounds correct.

[rocketfs 2]

Bert,You'll notice the thrust reduction altitude is adjustable : you can modify it in page 2. But if I remember well what a rw pilot told me, ICAO regulations make it mandatory to maintain at least 75% of full thrust until the take-off phase is over - ie 1500 ft above the ground. You can have derated power but it must be avove 75% of full thrust. Then, whether you take off at full rated or derated power, you'll apply thrust reduction, so prevention of engine damage is not the main factor here. Could the rw pilots in this thread please confirm this?Bruno

Euh.. I don't recall ICAO saying anything about 75% of max thrust but I'm not an expert.ICAO DOES define minimum standard climb rates (3,2 degrees or something?) and if not standard to be published on AIP and SID charts. They define how -departure- routes are to be designed in respect with obstacle clearance and surrounding airspace/traffic/aircraft type.75% seems a very strange number to me and cannot have anything to do with derated power settings or thrust reduction for B737 from T/O to climb thrust because these figures are normally much higher (in between 99,x and 8x,x percent). Ever tried to t/o a 737 with 75,1% thrust? If yes, try again with an engine failure after V1...good luck!But I'll repeat your question; any one else about the 75% number?Best Regards,Bert Van Bulck

I won't comment on ICAO regs, because all I pay attention to is the FAA. I will clarify, however, that preventing damage is not the main factor. The main factor would be preventing excessive wear (the same goes for the APU restrictions on using bleed 1 min after start and 1 min before shut down). More stress results in higher wear. Damage is really only an issue when operating outside of the engine's designed parameters. Engineers design with a certain percent margin in place so that even going outside of the envelope won't immediately cause a failure, but it will eventually happen if pushed too far or too long. Damage from use (with no external causes: FOD, volcanic ash, etc) is rare unless the engine is outside its normal limits, so it's really wear that is the prime concern.

I agree, main factor is wear (and cost). However, if an engine is operated longer time above "max continuous thrust" (which t/o thrust is mostly) engine damage is possible.Bert Van Bulck

[Spin737 102]

Bert,You'll notice the thrust reduction altitude is adjustable : you can modify it in page 2. But if I remember well what a rw pilot told me, ICAO regulations make it mandatory to maintain at least 75% of full thrust until the take-off phase is over - ie 1500 ft above the ground. You can have derated power but it must be avove 75% of full thrust. Then, whether you take off at full rated or derated power, you'll apply thrust reduction, so prevention of engine damage is not the main factor here. Could the rw pilots in this thread please confirm this?Bruno

The thrust reduction height varies with NADP-1 and NADP-2. Airports can specify thrust reduction in their noise abatement programs. NADP-1 is usually 1500', but NADP-2 is initiation of flap retraction, usually after 1000'. Int the US, it's usually 1000'.You're close on the derate, but not quite right. You can use the ATM (assumed temperature method) to get a thrust setting that is no less than 75% of the rated thrust. The rated thrust is whatever you select (22k, 24k, 26k, 27k Bump).For instance, let's say you're very light and you'd only need 16,500lbs of thrust. You'd look in the charts or the computer would do it for you and find that you could do a 22k T/O with an assumed temp of 60C. (75% of 22,000lbs = 16,500lbs). On the next flight, you're heavier and you'd need 23,000lbs. You couldn't use 22k, so you'd use 24k or 26k and use an assumed temp to reduce the thrust.

[Ralgh 43]

When the start switches are in the AUTO position it provides automatic ignition to selected igniters when the engine is running AND flaps are not up below 18,000 feet OR engine anti-ice is selected on.

[NG_Aviator 39]

When the start switches are in the AUTO position it provides automatic ignition to selected igniters when the engine is running AND flaps are not up below 18,000 feet OR engine anti-ice is selected on.

Thanks Tom, so if there is no auto position (as in screenshots so far), do you need to manually move the switch to CONT for takeoff, landing, under heavy rain and whenever anti-ice is on?

[Ralgh 43]

Thanks Tom, so if there is no auto position (as in screenshots so far), do you need to manually move the switch to CONT for takeoff, landing, under heavy rain and whenever anti-ice is on?

Yup that's the way I understand it. Actually that's exactly what it says in the LIMITATIONS section of our manual. Our 737s always had the auto position as long as I have been flying them so the only time we have to actually move the switch is in heavy rain. The limitations used to also include heavy turbulence but they removed that years ago.

[Spin737 102]

Ralgh, you still have to move them for engine start, right?We still have a note about Start Switches to Flight in severe turbulence. I think that comes straight from the AFM, though.

[Ralgh 43]

Yes we do have to move them to start.