NADP Takeoff thrust time limit
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From: Earth
NADP Takeoff thrust time limit
I was recently told ICAO requires aircraft flying NADP 2 (and maybe NADP 1 for all I know) to set climb thrust within 3 minutes of takeoff. I can’t find reference for this, does anyone have it?
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From: If this is Tuesday, it must be?
Thread Starter
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From: Earth
I’m asking because of the new HKG SID’s.
To make crossing restrictions some crews are maintaining takeoff flaps and climbing at ~ V2 + 10 to 4000 on NADP 2 runways. Thrust reduction on NADP 2 is based on flaps reaching 5 (selected at V2 + 40) while takeoff flaps are 10 or 20 for the 747. So, thrust reduction is not happening until 4000 when the first crossing restriction is met, which can take more than 3 minutes in a 980,000 lb airplane on a 35C day.
A genx2b67 failed and this technique was blamed due to it staying in takeoff thrust for 3 minutes (even though it’s rated to stay in takeoff thrust for 5 minutes or 10 if an engine failure has occurred on another engine).
To make crossing restrictions some crews are maintaining takeoff flaps and climbing at ~ V2 + 10 to 4000 on NADP 2 runways. Thrust reduction on NADP 2 is based on flaps reaching 5 (selected at V2 + 40) while takeoff flaps are 10 or 20 for the 747. So, thrust reduction is not happening until 4000 when the first crossing restriction is met, which can take more than 3 minutes in a 980,000 lb airplane on a 35C day.
A genx2b67 failed and this technique was blamed due to it staying in takeoff thrust for 3 minutes (even though it’s rated to stay in takeoff thrust for 5 minutes or 10 if an engine failure has occurred on another engine).
Eidolon
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From: Some hole
I’m asking because of the new HKG SID’s.
To make crossing restrictions some crews are maintaining takeoff flaps and climbing at ~ V2 + 10 to 4000 on NADP 2 runways. Thrust reduction on NADP 2 is based on flaps reaching 5 (selected at V2 + 40) while takeoff flaps are 10 or 20 for the 747. So, thrust reduction is not happening until 4000 when the first crossing restriction is met, which can take more than 3 minutes in a 980,000 lb airplane on a 35C day.
A genx2b67 failed and this technique was blamed due to it staying in takeoff thrust for 3 minutes (even though it’s rated to stay in takeoff thrust for 5 minutes or 10 if an engine failure has occurred on another engine).
To make crossing restrictions some crews are maintaining takeoff flaps and climbing at ~ V2 + 10 to 4000 on NADP 2 runways. Thrust reduction on NADP 2 is based on flaps reaching 5 (selected at V2 + 40) while takeoff flaps are 10 or 20 for the 747. So, thrust reduction is not happening until 4000 when the first crossing restriction is met, which can take more than 3 minutes in a 980,000 lb airplane on a 35C day.
A genx2b67 failed and this technique was blamed due to it staying in takeoff thrust for 3 minutes (even though it’s rated to stay in takeoff thrust for 5 minutes or 10 if an engine failure has occurred on another engine).
There is nothing special about the HKG SIDs, if you cannot make an SID altitude just let delivery know what you can do.
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From: IRS NAV ONLY
To make crossing restrictions some crews are maintaining takeoff flaps and climbing at ~ V2 + 10 to 4000 on NADP 2 runways. Thrust reduction on NADP 2 is based on flaps reaching 5 (selected at V2 + 40) while takeoff flaps are 10 or 20 for the 747. So, thrust reduction is not happening until 4000 when the first crossing restriction is met, which can take more than 3 minutes in a 980,000 lb airplane on a 35C day.
While technically it is true that thrust should be reduced with flap retraction, that's too much work for my little brain, and I prefer my capacity is to be used for something else, so we just let FMC and A/T do it at a specified level (we use 1500ft AAL). If climb gradient is an issue (fairly rarely on the 737), we can play around with thrust reduction and acceleration altitudes in the OPT to meet the SID requirements.
Keeping takeoff thrust (and probably full rated one at that) for 3 minutes routinely during normal takeoffs... I wouldn't want to be the one paying your mx bill, that's for sure.
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From: Somewhere
I’m asking because of the new HKG SID’s.
To make crossing restrictions some crews are maintaining takeoff flaps and climbing at ~ V2 + 10 to 4000 on NADP 2 runways. Thrust reduction on NADP 2 is based on flaps reaching 5 (selected at V2 + 40) while takeoff flaps are 10 or 20 for the 747. So, thrust reduction is not happening until 4000 when the first crossing restriction is met, which can take more than 3 minutes in a 980,000 lb airplane on a 35C day.
A genx2b67 failed and this technique was blamed due to it staying in takeoff thrust for 3 minutes (even though it’s rated to stay in takeoff thrust for 5 minutes or 10 if an engine failure has occurred on another engine).
To make crossing restrictions some crews are maintaining takeoff flaps and climbing at ~ V2 + 10 to 4000 on NADP 2 runways. Thrust reduction on NADP 2 is based on flaps reaching 5 (selected at V2 + 40) while takeoff flaps are 10 or 20 for the 747. So, thrust reduction is not happening until 4000 when the first crossing restriction is met, which can take more than 3 minutes in a 980,000 lb airplane on a 35C day.
A genx2b67 failed and this technique was blamed due to it staying in takeoff thrust for 3 minutes (even though it’s rated to stay in takeoff thrust for 5 minutes or 10 if an engine failure has occurred on another engine).
HKG SID requires 4000 and speed at 210 kt because of TERRAIN not NADP .In this situation you have to choose which NADP is practical,1 or 2 , normally 1 is suitable.Ok if you choose NADP 2 the acceleration is initiated at normal altitude to 210kt and thrust reduction is initiated at any point along acceleration segment even the first flap is not retracted.(In normal routine the easy way to do that is to select the next flap in take off ref page for thrust reduction and thrust is not reduced in this case) . Anyway if this SID is not practical , choose other SIDs or other RWs .No such NADP as you said in the world.
Last edited by Noknoipobin; 8th July 2025 at 11:04.
Thread Starter
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From: Earth
Ok, so the original premise of this thread was wrong, it turns out there is apparently a 3,000 ft AFE takeoff thrust limit per ICAO noise abatement procedures? At least this is according to my airline’s technical authorities. Can anyone point me to a reference for this? The closest I can find are statements such as:
“(6) Maintain the speed and thrust criteria as described in subparagraph 6 b(3) through 6 b(5) to 3,000 feet AFF or above, or until the airplane has been fully transitioned to the en route climb configuration (whichever occurs first), then transition to normal en route climb procedure”
It is coming up in HKG on the NADP-2 runways there, after the new SID’s were constructed in 2024 that have speed limits requiring takeoff flap settings to remain in place until ~6000 ft AFE at heavy weights. Normally the reduction to climb thrust happens at flaps 5 on NADP-2 (B-747 with flaps 10 or 20 takeoff settings) but we are now being instructed to manually reduce thrust at 3,000. This is being mandated irrespective of the 5 minute takeoff thrust limitation.
“(6) Maintain the speed and thrust criteria as described in subparagraph 6 b(3) through 6 b(5) to 3,000 feet AFF or above, or until the airplane has been fully transitioned to the en route climb configuration (whichever occurs first), then transition to normal en route climb procedure”
It is coming up in HKG on the NADP-2 runways there, after the new SID’s were constructed in 2024 that have speed limits requiring takeoff flap settings to remain in place until ~6000 ft AFE at heavy weights. Normally the reduction to climb thrust happens at flaps 5 on NADP-2 (B-747 with flaps 10 or 20 takeoff settings) but we are now being instructed to manually reduce thrust at 3,000. This is being mandated irrespective of the 5 minute takeoff thrust limitation.
Last edited by RandomPerson8008; 23rd January 2026 at 21:00.
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From: Hong Kong
Not a 747 pilot so can you explain that again? Are you saying you take off with flap 20 and you can't reduce thrust until after you've accelerated to flap 5? I thought the whole point of NADP was to take off, reduce thrust then accelerate (And if you can't make a restriction, tell ATC)?
Thread Starter
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From: Earth
Originally Posted by rudestuff;[url=tel:12026186
12026186]Not a 747 pilot so can you explain that again? Are you saying you take off with flap 20 and you can't reduce thrust until after you've accelerated to flap 5? I thought the whole point of NADP was to take off, reduce thrust then accelerate (And if you can't make a restriction, tell ATC)?
HKG for some reason uses NADP 2 all runways however they have SID waypoint restrictions ~6 miles from the runway that require 210 knots maximum. Flaps 5 selection speeds are usually ~230 at maximum takeoff weight.
If nothing is done, following a maximum weight takeoff, thrust reduction will not occur until passing roughly 4000-5000 ft on these SIDs unless an MCP switch is pressed or CDU entry made at the desired thrust reduction point in flight. There is also a 5 minute takeoff thrust limitation. Yet we are being directed by company to select climb thrust not later than 3000 ft AFE, we are told due to ICAO NADP profile requirements.
I am just asking if anyone has a specific reference for this “not later than” 3000 ft AFE thrust reduction requirement. 3000ft will typically be reached ~3 minutes after takeoff thrust application so the 5 minute time limit isn’t the reason.
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From: Earth
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From: Between a rock and a hard place
Never flown a 747 so not really sure what it can or cannot do at MTOW. To me it seems operators and procedure designers should sit down around a table and talk. I often get the impression procedure designers don't know what an aircraft is when they put a, seemingly, arbitrary "max 210 kts" 25 miles out on a SID over open water. Likewise I cannot understand operators/pilots so fixed on sticking to SOP that they can't flex an inch to comply with relatively mundane stuff.
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From: Europe
There is no ICAO NADP time limit for takeoff thrust. NADP is defined by altitude, not time: the first action (thrust reduction or acceleration) is at ≥ 800 ft AAL and the noise abatement procedure is usually completed by ~3,000 ft AAL (guidance, not a limit).
For both NADP 1 and 2 the first action is at 800 ft and the procedure is completed by 3,000 ft, with no time-based requirement.
The often-quoted “3 minutes” is a misinterpretation: many aircraft reach ~3,000 ft in about 2–3 minutes, which has been incorrectly remembered as a time rule. The only actual time limits are engine certification limits (5 minutes AEO, 10 minutes OEI).
B747-400: at heavy weights or with SID/obstacle constraints it is normal to hold takeoff thrust above 3,000 ft and exceed 3 minutes; this is not an NADP violation as long as engine limits and company SOPs are respected.
Bottom line: there is no ICAO “3-minute NADP rule.”
Pertinent document
For both NADP 1 and 2 the first action is at 800 ft and the procedure is completed by 3,000 ft, with no time-based requirement.
The often-quoted “3 minutes” is a misinterpretation: many aircraft reach ~3,000 ft in about 2–3 minutes, which has been incorrectly remembered as a time rule. The only actual time limits are engine certification limits (5 minutes AEO, 10 minutes OEI).
B747-400: at heavy weights or with SID/obstacle constraints it is normal to hold takeoff thrust above 3,000 ft and exceed 3 minutes; this is not an NADP violation as long as engine limits and company SOPs are respected.
Bottom line: there is no ICAO “3-minute NADP rule.”
Pertinent document
Thread Starter
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From: Earth
Ok, thanks, so it seems you all are suggesting that the airline may have made up the ICAO/NADP 3,000 ft takeoff limit as well as the initial 3 minute supposition. I understand the airline doesn’t want the engine in takeoff thrust for any longer than necessary for engine reliability. It seems like that alone would be a good enough reason to select CLB thrust when they want us to so I’m not sure why we needed to go through all of this. Thanks for everyone’s help, I’ll go back to radio silence.