A retired TWA captain told me that at heavy weights he would have to level off at 1500 feet above field level in order to build up speed for flap retraction or sometimes just barely climb. I think he flew 747-100s. Just wondering if now a days jetliners have trouble both climbing and building up speed after takeoff.Is that a thing of the past? Guessing it depends on the plane and the circumstances.

convair880mfan wrote:

A retired TWA captain told me that at heavy weights he would have to level off at 1500 feet above field level in order to build up speed for flap retraction or sometimes just barely climb. I think he flew 747-100s. Just wondering if now a days jetliners have trouble both climbing and building up speed after takeoff.Is that a thing of the past? Guessing it depends on the plane and the circumstances.

Most airliners will level off slightly at around 1500ft to begin building up speed, the old slightly underpowered 747-100's may well have been struggling a bit, I know even the -400 at high weights will have a flaps up speed of over 250kt.

I flew 747-100s, -200s, and -400s. The -100s were particularly undepowered (especially since they were freighters, which typically take off at higher weights). We routinely selected vertical speed 200 feet per minute at flap retraction altitude in order to build enough acceleration to get to flap retraction speed. If it was hot and we were heavy, we used vertical speed 0, i.e. flying level, in order to accelerate an clean up!

Never flown a quad - but modern twins climb quite happily during acceleration/flap retraction on both engines - even when heavy and with reduced climb thrust.

OTOH acceleration on single engine does require level (or nearly level) flight.

P.S. the closest to level acceleration was when I flew ATRs in India (so generally in hot weather) - the SOP was to accelerate at 800ft AAL and the climb rate was probably around 500ft/min, if not less. It looked pretty cool both from inside and outside…

Yes in a heavy A343 out of JNB in the summer

Heavy 727-200 with -9 engines when hot and high, yes for sure.

Trying to understand to understand the process. After rotation and wheels up, the aircraft is then leveled, with flaps extended, until speed builds up?

Wouldn't retracting the flaps help with reducing drag in order to increase speed (clean wings), or is this necessary to due to needing to overcome thrust/weight limitations by adding lift at slow speeds.

Last time I did the math for NACA airfoils with flaps was in my undergraduate program, with Apple Mac IIs and Pascal. I am sure there are easy to use apps that show the math of what happens, or I could start using X-Plane again to try it out safely.

(Just checked out the cost of PPL programs in case next year I can find an opportunity to do what I wanted to do years ago)

boacvc10 wrote:

Trying to understand to understand the process. After rotation and wheels up, the aircraft is then leveled, with flaps extended, until speed builds up?

Wouldn't retracting the flaps help with reducing drag in order to increase speed (clean wings), or is this necessary to due to needing to overcome thrust/weight limitations by adding lift at slow speeds.

Really depends on the aircraft. Having flown in a flight simulator, I note that a Boeing 747-400 at maximum take-off weight struggles to climb and accelerate at the same time. At lighter weights, this isn't an issue.

The only model of the 747 I haven't flown is the -8. However, the nice thing is they all tend to fly the same. The 100, when heavy was certainly not a stellar performer. But with JT9-7A power, it didn't require a level off at MTOW of 750,000 lbs., but the rate of climb certainly had to be reduced. If I remember correctly, the pitch was reduced to about 8-9 degrees on the ADI and the aircraft would do its best to accelerate. The 200 with 7F engines certainly wasn't a stellar climber either. But, the 200B with R4G2 engines and the 400 did just fine with departure at MTOW.

AirKevin wrote:

boacvc10 wrote:

Trying to understand to understand the process. After rotation and wheels up, the aircraft is then leveled, with flaps extended, until speed builds up?

Wouldn't retracting the flaps help with reducing drag in order to increase speed (clean wings), or is this necessary to due to needing to overcome thrust/weight limitations by adding lift at slow speeds.

Really depends on the aircraft. Having flown in a flight simulator, I note that a Boeing 747-400 at maximum take-off weight struggles to climb and accelerate at the same time. At lighter weights, this isn't an issue.

Anecdotally speaking, on a UA 744 out of HKG for ORD in 2011 and listening to channel 9 (the good ole days...) we departed to the southwest, flew for a few miles then turned back to the north and I specifically remember the female ATC with her British accent asking the pilots to climb faster. I don't remember the actual verbiage but the exchange was cordial and the pilot basically told her we were at max climb for the weight, etc

tb727 wrote:

Heavy 727-200 with -9 engines when hot and high, yes for sure.

Not a high altitude airport at all, but remember vividly watching thousands of B722's depart IAH working in the tower. Our hot summer days in Houston with them going to places like LAX, SFO, SEA when I'd switch them to departure and they'd start retracting the flaps it looks like they were sinking (which of course they weren't), but new controllers would always ask "are they going to climb".

boacvc10 wrote:

Trying to understand to understand the process. After rotation and wheels up, the aircraft is then leveled, with flaps extended, until speed builds up?

Wouldn't retracting the flaps help with reducing drag in order to increase speed (clean wings), or is this necessary to due to needing to overcome thrust/weight limitations by adding lift at slow speeds.

Last time I did the math for NACA airfoils with flaps was in my undergraduate program, with Apple Mac IIs and Pascal. I am sure there are easy to use apps that show the math of what happens, or I could start using X-Plane again to try it out safely.

(Just checked out the cost of PPL programs in case next year I can find an opportunity to do what I wanted to do years ago)

A takeoff profile has a thrust reduction altitude, and an acceleration altitude.

At thrust reduction altitude, the takeoff thrust is reduced to climb thrust, and at acceleration altitude, the aircraft accelerates to climb speed. Sometimes there isn’t enough thrust to accelerate and climb. We’re not targeting a specific climb rate.

Flap retraction occurs on schedule as the aircraft accelerates to climb speed. As we retract the flaps, climb rate varies throughout the whole process, it’s not anything like the flight track logs you find on the flight tracker websites.

Generally thrust reduction and acceleration is 1000ft AFE at my air carrier. And climb speed is 250kts. So at 1000ft AFE, the thrust levers are retarded from TOGA/FLX to CLB and the aircraft accelerates to 250kts. With flap retraction occurring as the speed increases from V2+10kts/150kts to 250kts or whatever speed is dictated by the departure procedure.

Other air carriers or airports may have a different takeoff profile. The terms you’ll hear are NADP 1 and NADP 2. At Orange County airport in California, the thrust reduction altitude is 800ft AFL or 855ft MSL and acceleration is at 3000ft AFL or 3055ft MSL.

convair880mfan wrote:

A retired TWA captain told me that at heavy weights he would have to level off at 1500 feet above field level in order to build up speed for flap retraction or sometimes just barely climb. I think he flew 747-100s. Just wondering if now a days jetliners have trouble both climbing and building up speed after takeoff.Is that a thing of the past? Guessing it depends on the plane and the circumstances.

Not particulary with all engines operating, it would not be unusual to level off in an engine out situation for acceleration and flap retraction.

convair880mfan wrote:

A retired TWA captain told me that at heavy weights he would have to level off at 1500 feet above field level in order to build up speed for flap retraction or sometimes just barely climb. I think he flew 747-100s. Just wondering if now a days jetliners have trouble both climbing and building up speed after takeoff.Is that a thing of the past? Guessing it depends on the plane and the circumstances.

That's correct, depending temperature and field elevation, the early 747-100's and even more the first 747-200B's, both powered with PW JT9D-3AW (wet rating 45.000 lb ) were severly underpowered.

I have operated these early 747-200B's at MTOW of 351.500 kgs (775.000 lb) from 1978, powered by upgraded PW JT9D-7W (wet rating 47.000 lb) and even with these engines the acceleration was very poor, because after 2.5 minutes you had to switch off the water injection, reducing the T/O power to dry GA thrust for the next 2.5 minutes.

But i'm aware of the stories from the flight crews that had operated the first 747-200B's at 775.000 lb MTOW with these early -3AW's during 1970-1974 (only climbing because the earth was round !)

In a N-1 situation (very frequently with the high IFSD rate at that time), the climb was reduced to zero and with Max Continuous thrust a very slowly speed increase was only possible.
(In the simulator with a nasty instructor you had to deal with a temperature inversion during the N-1 to make things even more difficult !)

See Boeing 747-1/2/300,SP -- ACAPS -- FAR Runway length requirements 747-100-200/ -3AW at page 74 & 75 : https://www.boeing.com/resources/boeing ... _123sp.pdf

B744 will climb at approx. 500fpm during the acceleration (cleanup) segment, this reduces slightly during the turn. Legal requirement for 3rd segment is "positive gradient". Acceleration height varies due to noise abatement, operator specifics, obstacles etc. Minimum clean speed is up to 280kts below 10,000ft so in case high speed has not been approved, flaps 1 or even 5 are used below that altitude. Flying with flaps extended is always less optimum than clean

Dufo wrote:

B744 will climb at approx. 500fpm during the acceleration (cleanup) segment, this reduces slightly during the turn. Legal requirement for 3rd segment is "positive gradient". Acceleration height varies due to noise abatement, operator specifics, obstacles etc. Minimum clean speed is up to 280kts below 10,000ft so in case high speed has not been approved, flaps 1 or even 5 are used below that altitude. Flying with flaps extended is always less optimum than clean

That is the climb rate I usually see when loaded. But the 744 and 748 definitely can achieve a higher climb rate. I’ve noticed the 74 can be quite aggressive with this acceleration segment of the climb it needs from time to time. I’ve definitely seen 1000 to 1500 fpm in this segment.

T54A wrote:

Yes in a heavy A343 out of JNB in the summer

Pretty much any heavy quad out of JNB in summer tbh.

KingOrGod wrote:

T54A wrote:

Yes in a heavy A343 out of JNB in the summer

Pretty much any heavy quad out of JNB in summer tbh.

Yeh probably. The A346 wasn't too bad though

T54A wrote:

KingOrGod wrote:

T54A wrote:

Yes in a heavy A343 out of JNB in the summer

Pretty much any heavy quad out of JNB in summer tbh.

Yeh probably. The A346 wasn't too bad though

I worked JNB outbounds for quite some time and the QF 744 to SYD and SA 744 to HKG stick out in my mind for the worst climbs literally ever experienced. Besides the YK40 at any phase of flight and the CRJ2 above F290

KingOrGod wrote:

T54A wrote:

KingOrGod wrote:

Pretty much any heavy quad out of JNB in summer tbh.

Yeh probably. The A346 wasn't too bad though

I worked JNB outbounds for quite some time and the QF 744 to SYD and SA 744 to HKG stick out in my mind for the worst climbs literally ever experienced. Besides the YK40 at any phase of flight and the CRJ2 above F290

I bet the 747-100 / 200 were worse than the -400 though.

I'm a little surprised that this discussion has not taken into account the segmented takeoff climb profiles or the oft times related noise abatement procedures.

Modern airliners, by definition must meet certain criteria to be compliant with obstacle clearance after the takeoff segment has been completed (35' @ V2).

If the second segment can be completed safely, then the acceleration to transition to a climb configuration will take place. That typically involves an acceleration to a safe speed to retract. The FAA lowest height that that can occur is 400' AAE. Many companies use an arbitrary "Level Off Height" of 1000' AAE. My last contract job had that blanket policy. Where it bit them in the butt was in JNB/FAOR where the airport elevation was about 5,500' ASL. They were severely weight restricted (i.e. payload) to meet their WAT limits and their takeoff time limitations on takeoff thrust settings (5 minutes). With an in depth re-analysis, a lower level off height of 800' AAE and the 10 minute takeoff thrust limit for the engines installed on those B763's they operated, resulted in a net increase of nearly 8 metric tonnes of payload. All for no impact on safety.

So I am still at odds to the questions asked in this thread. Why are they being asked when the answers are already out there?

747-200 with JT9D-7J what performance did it have during initial acceleration while cleaning the wing? Was level flight necessary at MTOW?

lh777 wrote:

747-200 with JT9D-7J what performance did it have during initial acceleration while cleaning the wing? Was level flight necessary at MTOW?

Almost all JT9D-7J engines are modified from earlier -3A-7,7A and 7F engines. This was accompliced by a modified HPT (with directional solidified blades),
Thrust is 48,560 lb (50,000 lb ideal), dry (no water injection anymore !) and Max. EGT is 985 degr C Tt6.

The MTOW at the 747-200B series with JT9D-7J engines installed was approx 800.000 lbs.
See page 9 : https://www.boeing.com/resources/boeing ... _123sp.pdf

However later the MTOW was further reduced for stage 3 (noise) compliance and even 747-200B's with JT-9D-7F engines were upgraded to -7J standard, because :

A 747 with JT9D-7F engines is stage 3 certified up to TOW 750.0000 lbs (50.000 lbs penalty)
A 747 with JT9D -7J engines is stage 3 certified up to TOW 770.000 lbs (30.000 lbs penalty.)

Note : For the JT9D-7J, there is a paper modification that improves performance of the -200B when operating under Stage 3 restrictions. The upgrade is achieved by moving the centre of gravity, combined with a change in the aircraft trim. This allows a lower thrust setting to be used, resulting in lower noise levels at higher MTOW, increasing MTOW from 770,000lbs to 791,000lbs


Depending actual TOW, OAT, field elevation, the accelleration was normal. (almost never level flight was needed)

Is this an AEO or OEI case? Every plane at the WAT limit with an engine inoperative will level off to accelerate, AEO not usually.

GalaxyFlyer wrote:

Is this an AEO or OEI case? Every plane at the WAT limit with an engine inoperative will level off to accelerate, AEO not usually.

All engines operating (AEO), with N-1 : level acceleration.

As a technique as well, at heavy weights its nice to accelerate away from stall speeds as you clean up, even if that means a temporary level off.