B737NG F/D's on Initial Climb Out.

[B737NG_Pilot]

Automatic Flight Takeoff and Climb

There are certain times at LIFT-OFF during the initial climb out, the F/D pitch command at times indicates 20 degrees of pitch instead of 15. And latter reduces to 15? Is this something to do with the Rate of Rotation.

Also is it safe to pitch up to 20 degrees, following the F/D guidance ?

[172_driver]

FD commands V2+20.. at least in our fleet, but I have myself always wondered if this is generic 737NG or a customer option.

If you are climbing into a strong headwind it's normal. You may want to restrict your pitch to max 20. Your company may have a saying in what they want you to do.

[de facto]

Most probably you under rotated or as said you got into strong headwinds.
Possibly also if you are relatively lower weight and high thrust(no ASS).
If the FD go back in a short period of time from 20 to 15 its probably due to an under rotation/speed too high,after corrected it goes back to a normal 15 deg(standard ASS and weight ratio).
Most airlines restrict the pitch by pilot action to 20 degrees,ie disregard FD).
Remember 25 degrees pitch up is considered an upset and needs to be dealt with as laid down in your QRH.

Your captains dont teach you anything?worried to ask them?

[sheppey]

Also is it safe to pitch up to 20 degrees, following the F/D guidance ?


Never completely put your trust in flight directors. They are an aid to navigation - not the be all and end all as some pilots think. Know the correct pitch attitudes for the condition of flight and stick to that. Blindly following the FD needles has caused many pilots grief. Once you have learned to fly competently on raw data (FD off), then you will soon be aware if the FD is over-reacting to hasty pitch angle movements or leading you up the garden path. Even the manufacturer Boeing in the 737 FCTM recommends turning off the FD if the FD commands are not to be followed.

[Lord Spandex Masher]

Remember 25 degrees pitch up is considered an upset and needs to be dealt with as laid down in your QRH.

ONLY if it is unintentional.

[de facto]

Correct but its a fine line between unintentional and unaware of a potential threat.
Now the recovery of the 'upset' can be done in less drastic or different manner than the nose high actions as laid sown.For example if AP engaged,command increase of speed which will command the AP to reduce pitch.
If you approach a stall unintentionally,i hope you would recover as well:E

[Lord Spandex Masher]

Of course, I'd consider unaware the same as unintentional in this case.

I'm just highlighting that a blanket - 25 degrees = upset is not correct.

Some of flying I do on the 737 I regularly see a lot more than 25 degrees, if I was to treat that as an upset then I'd never get the job done and that would be a shame because it's a lot of fun!

[de facto]

And if i had 25 deg every day doing my job,my QAR mailbox would explode:p
Taking my coat and out for some well deserved fresh air:ok:

[ImbracableCrunk]

20 degree ANU is also a "gate" for some FOQA programs where it starts looking at bank angle.

My company wouldn't care, but some Asian carriers would be talking to you if you bank over 15 Degrees with 20 ANU.

[latetonite]

Back to the original question.

You will get an original pitch up indication of 15 degrees NU.

This should result in a V2 plus 20 speed.

If you underrotate, you are not following the FD, but the FCC does not know that. In fact this computer is made to believe that you as a competent pilot are following the FD command.

The computer only learns quick that a 15 degree NU command results in a higher than V2+20 speed.

Therefore the clever computer will give you now a 20 degree NU command, to try to satisfy the speed requirement.

When you now start pulling on the stick, speed will come back. The now happy computer will command the FD to come down, and meet you somewhere halfway..

If you rotate as you should, you will not see The FD showing you 20 degrees NU, unless you ferry the plane with TO trust.

[Denti]

The initial 15° initial NU is not a command by the way, if you use derate plus ATM (and probably improved climb speed schedule as well) an initial pitch of around 12° is likely enough, more would lead to a speed drop. There is a reason why there is a Note in the FCM which says that the FD pitch command is not to be used for rotation.

To be honest, pitch in excess of 20° seems to be rare in the NG, slightly more common in the 700 than the 800. However it was quite common in the classic during initial climbout, up to 25° was considered perfectly normal.

[flyhardmo]

Never completely put your trust in flight directors. They are an aid to navigation - not the be all and end all as some pilots think. Know the correct pitch attitudes for the condition of flight and stick to that. Blindly following the FD needles has caused many pilots grief.:D:D:D

Spot on Sheppey.
Keep your scan up and be prepared to fly through the flight director.

[latetonite]

@ denti: if you use derate, plus max assumed, you FD's will still give you a correct pitch control. Ofcourse not at rotation, but in initial climb. Thanks, I have a FCTM.

You probably switch them off during TO, no?

And, while during an CatIII landing, make sure you look through them, just to be sure?

[172_driver]

Isn't it quite easy really?

FD commands MCP (normally V2) + 20 kts and the pitch command will be whatever it will be. Light weight/high thrust the pitch command will naturally be higher than high weight/low thrust.

Is the question not answered now?

[flyboyike]

Isn't it quite easy really?

FD commands MCP (normally V2) + 20 kts and the pitch command will be whatever it will be. Light weight/high thrust the pitch command will naturally be higher than high weight/low thrust.

Is the question not answered now?


It's quite easy for someone who actually flies, not just claims to fly.

[Capn Bloggs]

172 Driver and flyboymike, the question as I see it is why the bars drop back from 20° to 15°, not why they are sometimes 20° and other times 15°.

[flyboyike]

Who cares what they drop to (or don't drop to)? I don't even look at the F/D on take off, I look at my airspeed and the trend vector thereof.

[Capn Bloggs]

We are cranky tonight...

[latetonite]

The FD s drop as the FCC sees the V2 +20 requirement being achieved.
Read my pevious post.
Opposite, if one would climb extremely shallow after liftof, th FDs would indicate their max pitch.

[flyboyike]

Fly the airplane, not the flight director, then you won't have to worry about what it's dropping to.

[172_driver]

172 Driver and flyboymike, the question as I see it is why the bars drop back from 20° to 15°, not why they are sometimes 20° and other times 15°

Agree.. but still think that "FD commands MCP (normally V2) + 20 kts and the pitch command will be whatever it will be" gives the answer.

To the OP, the other week it was very windy over Europe. Climbing into a 40-50 kts headwind I think the airspeed quickly increased to close to 200 kts (with V2+ 20 being something like 160-170). You can imagine the FDs climbed through the ceiling and were of very little use. Once the wind stabilized and airplane "caught up" with the energy gain the FDs slowly came back to center. I never pitched above 20 deg ANU because my company doesn't like it.

[Denti]

@ denti: if you use derate, plus max assumed, you FD's will still give you a correct pitch control. Ofcourse not at rotation, but in initial climb. Thanks, I have a FCTM.

Then i humbly suggest to read it, your post above said something else:

You will get an original pitch up indication of 15 degrees NU.

This should result in a V2 plus 20 speed.

That is of course not always correct, actually quite often. 15° does usually not result in V2 plus 20. However, after initial pitch up to a achieve said speed the flight director will shortly follow and indicate the same. If one uses it at all.

You probably switch them off during TO, no? Sometimes i do, sometimes i don't. As the company actively encourages us to fly without FD and autopilot to keep ones scan and skills it is up to us what we use.

And, while during an CatIII landing, make sure you look through them, just to be sure?

Monitoring if the autoflight system does its job? Of course, that is what i am paid for after all. Theoretically from 200ft until taxi speed we can go to sleep though as any failure (including engine failures) will result in a safe landing and rollout, but of course we still monitor the system as dual failures still can lead to unsafe conditions.

[latetonite]

Ok Denti,

I see you try to negotiate a lot.

In an answer to point one. My post above did not say something else. I presume we are not discussing rotation here.
I do read the FCTM quite a lot. In fact I am teaching from it 5 days a week.
Even the misconceptions I point out.

Second quote: If I read your comment well, your are suggesting the FD will follow the pitch you are flying? You do not believe that yourself, Do you?

Point three: your company does encourages TO without FD? And you practise that to prove you can rotate better, counting three degrees per second? I hope you are aware that your fellow new copilots will probably crash doing this in LoVis TO, given the remote condition that an engine fails.

I trust you make a note in your speech to the passengers, that they are lucky today in this bad weather that they have a good pilot who does not put trust in his instruments, and is honing his hand skills a bit.

In the last referral, catIII landings, you monitor failures of the 'system', you said.

But you trust letting the FDs command the autopilot, and land your flying machine, even on one engine. We have those planes too, but me maybe being not so talentfull as you, I do not see if the FD shows correct pitch. However, as we have two FDs , with two FCC behind them, I trust them. And let them bring me safe to the ground.

Not believing the FD during TO, but betting your life on them during autoland in LoVis, is a bit hypocrite, I think.

[flyboyike]

Point three: your company does encourages TO without FD? And you practise that to prove you can rotate better, counting three degrees per second? I hope you are aware that your fellow new copilots will probably crash doing this in LoVis TO, given the remote condition that an engine fails.



I would hope the new copilots' not crashing after an engine failure wasn't dependent on the F/D. After all, it can fail, too.

[172_driver]

latetonite,

To me it sounds like you want to misunderstand on purpose here.

I too think the FDs can be a bit over-sensitive on initial climb out and by looking through them, setting the attitude you think will be right for the weight/thrust, the FDs will usually come to sense and settle down quite close to where you put the nose.

[sheppey]

quote: Sometimes i do, sometimes i don't. As the company actively encourages us to fly without FD and autopilot to keep ones scan and skills it is up to us what we use. quote:


That cheers me up greatly. At long last a company that actually encourages its pilots to minimise automation addiction by flying normally, rather than by the magenta line.

[latetonite]

Sheppy, got your point. But there is no magenta line on my FD.

We are discussing TO here. In a modern airline with pax onboard.

Really want to see the airline which encourages raw data TO in daily operations.

Not that I do not know how it goes: In my career I have been flying 3 commercial A/C types as PIC, not even equipped with a F/D.

And quite a few more without an FMS.

[RAT 5]

B737NG PILOT:

I'll add my tuppn'yworth for your consideration. First: DO NOT rotate into the FD. Rotate to an attitude; i.e. look through the FD. The target is 15degrees. The FD commands a minimum of V2+15 to a max V2+25. This is on climb-out after the gear is up. Hence the initial target attitude. You will find that if you select a thrust which equals your weight, i.e. you use minimum thrust the FD will stabilise at 15 degrees eventually. If you over rotate the IAS will be <V2+15 and the FD will lower the attitude to accelerate to V2+15 then climb-out at that speed. If you under rotate, or rotate late, the IAS may be >V2+25 and the FD will eventually guide an increase in attitude to reduce IAS back to V2+25. It will then most likely stabilise at 15 degrees again. If you rotate properly you will find that you are at V2+20 and the FD will maintain this with 15 degrees NU.
If you use more than minimum thrust the initial rotation is still 15 degrees, but the excess thrust will allow a climb-out at V2 +20 with higher than 15 degrees. The FD will guide this attitude. It looks at many performance parameters to give correct guidance.
If you rotate such that the speed at liftoff is >V2+25 beware and DO NOT rotate to FD's as this will cause a rapid drop in IAS and a porpoise pitch climb-out. Above 20 degrees the drop in IAS is VERY rapid; and why would you want to go above 20degrees? Either you have screwed up the rotation and be at too high IAS, or you are way over powered. Either way your initial climb-out trajectory will be more than enough. If you are at so high an attitude the IAS will reduce quickly and then the FD will command a strong reduction in attitude to maintain V2+25. This can be quite uncomfortable.

A single continuous rotation at the correct rate to 15degrees, started at Vr should result in V2+20, and after the gear is up you'll find the FD maintains this with 15 degrees is weight matches thrust. Be aware if you are over powered and then the resulting extra 1 or 2 degrees is not confusing. BUT always use the initial 15 degrees.
Note" this is for F5 takeoffs. F15 may be 1-2 degrees lower.

[Lord Spandex Masher]

and why would you want to go above 20degrees?


What's wrong with going over 20 degrees if you need it?

Either you have screwed up the rotation and be at too high IAS, or you are way over powered.


Occasionally I am required to carry out a full power take off in an empty, and I mean empty, aircraft with 5 tonnes of fuel on!

Either way your initial climb-out trajectory will be more than enough.

In the above case you need the pitch to control the speed otherwise you get very close to the flap limiting speed before you can say P45.

[latetonite]

There is some truth in most replies, however, be aware that your carefull calculated V speeds go immediately out of the window if you do not rotate and climb correctly.

[RAT 5]

Occasionally I am required to carry out a full power take off in an empty, and I mean empty, aircraft with 5 tonnes of fuel on!

In the above case you need the pitch to control the speed otherwise you get very close to the flap limiting speed before you can say P45.

Why do you need to maintain full power for so long. Reducing power would allow reduced attitude etc. I hope this was performed with a very high SID cap. The vision of a home sick angel comes to mind. It used to be that a regular full power takeoff was required to confirm it was available and test the engine. Surely you don't need to maintain it for the full 5 mins. If not then you could reduce power to something more appropriate. I would have thought full power with a very light a/c was more a test pilot manoeuvre. Full power confirmations could be done easily by a line pilot on a more normal loaded a/c. This occasional testosterone fuelled takeoff might not be allied to the original question, which I'm sure was more line orientated on a normal day.

[Lord Spandex Masher]

My point is that there are no dragons beyond 20/25 degrees. It's not an upset and it's not dangerous. Most opinions are that exceeding 20/25 degrees pitch causes voodoo to happen. I'm just highlighting that it doesn't.

I'm required to carry out these take offs as part of an air test schedule but as we fly with standard line FOs we have to use standard procedures and there're other parameters to be monitored whilst at full power.

I accept that that isn't relevant to line ops and that I've strayed from the original topic but occasionally your line pilot will be asked to ferry or position an empty aircraft and may need to use full power. I think it's important to highlight that you won't fall out of the sky if you exceed 20 degrees and quite often it makes your day a lot easier if you do.

[BOAC]

I think the 73 Jurassic used to say
"Limit pitch to 20 degrees for passenger comfort"

Of course, when your 'pax' were sitting on trays.................:D

[latetonite]

Notwithstanding the passengers and crew in the cabin, I would not mind pitching 45 degrees NU, if it would result in a steady V2+20.

[RAT 5]

While your at it why not roll and pull through for a reverse cuban 8?

[flyboyike]

In the US it's called the Greater Antilles Eight, due to the embargo.

[latetonite]

Personally, I would not mind. At least something different.

[Denti]

We are discussing TO here. In a modern airline with pax onboard.

Really want to see the airline which encourages raw data TO in daily operations.

What is so special about it? It is basic airplane flying 101. Is the training in your company really so bad that they cannot trust their own pilots to do basic airplane handling? I don't doubt that you're able to do it with your background, but SOPs that actively discourage pilots from basic flying are a sure sign of a huge training deficit.

Just for reference, that is what our 737 FCOM says under the header Autopilot/Autothrottle Policy:

Continuous use of automatic systems leads to loss of basic knowledge of power settings/pitch attitudes and reduces the ability to fly accurately with a low workload. Pilots should therefore regularly fly the aircraft manually, with emphasis on manual departures/ approaches with and without the flight director.

Some never use the FD except during low vis operation (FD is not required for AP usage), some take a more moderate view and do every now and then take offs and approaches without using the FD.

Quite true by the way that wrong rotation and initial climb out can invalidate performance figures, our -800 performance is based on 2°/sec rotation rate and the -700 on 2,5°/sec. Unlike during the classic days we do not fly the short version (600) as it doesn't make any commercial sense, but performance would be based on 3°/sec.

[Aluminium shuffler]

First of all, there is nothing wrong with prudent and appropriate raw data departures. Some people seem to think that the wing bolts are connected to the FD switch. If Boeing thought that raw data flying was dangerous, they wouldn't fit the switch... Suggesting that all the performance calculations are nullified by flying raw data displays an immense lack of confidence in the individual's flying ability as well as their understanding of how everything works.

Secondly, the received wisdom is that the pitch attitude is not to exceed 20 degrees NU. The reason for this is to give you a decent opportunity to get the nose down without rapid speed loss if an engine fails and also to allow for wind sheer - it has nothing to do with comfort levels. Going beyond 20 degrees is needless and most companies' OFDM systems would be pinging off. I certainly wouldn't be happy with a colleague who did it without very good reason. Pitching higher sounds like show boating to me.

Third, the FD initial 15 degree NU command is only a rudimentary aiming point for rotation, and it guarantees nothing. It is a conservative pitch angle which will be modified once the FCCs catch up with the aircraft's actual performance. Commands above 20 degrees should only be followed to the 20 degree line.

Fourth, any pilot that blindly follows the FD without "looking through" it to verify against the performance data that suitable attitudes are being commanded is a fool. FDs are very useful but not infallible and they are reactive, not pre-emptive.

Fifth, FD commands aren't always displayed proportionately - if the FCC thinks you are not responding fast enough, the commands become exaggerated to gain your attention., and if you follow them fully you will be over-controlling the aircraft.

[Centaurus]

Fourth, any pilot that blindly follows the FD without "looking through" it to verify against the performance data that suitable attitudes are being commanded is a fool. FDs are very useful but not infallible and they are reactive, not pre-emptive.


"Looking through" the flight director presentation is quite difficult since most of the time the FD is being used means the pilot is concentrating on keeping the needles centred and watching for the slightest vertical or lateral movement. In my experience many new pilots to type are spooked as they try to centre the needles and because of their intense concentration on needles in a tiny square symbol on the ADI, they lose all awareness of the true pitch attitude behind the needles.

This is especially so when conducting an engine failure at VR. The fact is very few simulator instructors whether current check pilots or not - will take the trouble of hopping into a control seat and actually demonstrate how to fly the engine failure. They are mostly perfectly content to watch the candidate lose the plot due to chasing the FD needles, over or under controlling on elevators, ailerons and rudder pedals and then from the back of the simulator, loudly criticise the candidate. Or just as bad, try to "talk them through"

IMHO if you have to resort to "looking through" the FD display in order to see the real nose attitude hidden behind the FD needles, then it is better to immediately switch off the FD to get a clean unobstructed look at the ADI attitude. Then at leisure turn the FD back on when it suits. FD's are an over-rated instrument system that have the potential to, and have led to, loss of instrument flying situational awareness

[latetonite]

Cannot agree more.

[Lord Spandex Masher]

Secondly, the received wisdom is that the pitch attitude is not to exceed 20 degrees NU. The reason for this is to give you a decent opportunity to get the nose down without rapid speed loss if an engine fails and also to allow for wind sheer - it has nothing to do with comfort levels. Going beyond 20 degrees is needless and most companies' OFDM systems would be pinging off. I certainly wouldn't be happy with a colleague who did it without very good reason. Pitching higher sounds like show boating to me.

What?! Suddenly at 20.01 degrees we can no longer recover from wind sheer or control our speed following an engine failure?

[latetonite]

People seem to get confused mixing angle of attack and pitch attitude. Flying is not taught academically anymore, but by SOPs.

[latetonite]

Quote: "Fourth, any pilot that blindly follows the FD without "looking through" it to verify against the performance data that suitable attitudes are being commanded is a fool. FDs are very useful but not infallible and they are reactive, not pre-emptive." Unquote.

We are talking about subtle differences hopefully, a few degrees at most. Now, if you want to compare them with the available performance data in Vol.1 during your take off, I wish you and the airline good luck.

[flyboyike]

"Looking through" the flight director presentation is quite difficult...


Not really, not if you remember that you're paid to fly the airplane and not the F/D.

[latetonite]

Flyboyike:

Trust you apply a QNH correction as well.

After all, putting the correct pitch and getting the targeted lift, to obtain the required climb gradient, is WAT related.

Me, I take the liberty not to do that. And it works fine since many years.

[flyboyike]

I'm sorry, what?

[Lord Spandex Masher]

Secondly, the received wisdom is that the pitch attitude is not to exceed 20 degrees NU. The reason for this is to give you a decent opportunity to get the nose down without rapid speed loss if an engine fails and also to allow for wind sheer - it has nothing to do with comfort levels. Going beyond 20 degrees is needless and most companies' OFDM systems would be pinging off. I certainly wouldn't be happy with a colleague who did it without very good reason. Pitching higher sounds like show boating to me.

Latetonite, I'm still waiting for you to explain why you cannot recover from wind sheer or en engine failure above 20 degrees pitch.

[latetonite]

You can wait for that long time, as I do not recall saying that.

[Lord Spandex Masher]

Well perhaps an explanation of the above quote of yours.

[latetonite]

The above quote is not mine.

[Lord Spandex Masher]

Ah yes, mistaken identity. Sorry about that.

[latetonite]

No worries.

[Aluminium shuffler]

You can recover from that far nose up, but the recovery will be bigger and need more time and potentially more altitude, commodities you may not have just after take off. Granted, the margins between stalling attitude and commanded attitude may be similar for a FD command of 18o when heavy and 25o when light, but you don't need to be pushing the aircraft close to its performance capability when light, and you're increasing the chance of triggering TCAS, so why do it when 20o will give all the performance and more than you need?

Centaurus, I both agree and disagree (mildly) with you. ;) I agree that FDs are not infallible, and that they have led, along with FMCs and other automation, to a loss of basic SA and flying skills. I only disagree that they're hard to look through - as long as the rest of the instrument scan is maintained to corroborate and anticipate the FD commands, then I think it's not a difficult thing to do. Shame so many blindly follow them, failing in the rest of their scan.

[latetonite]

Aluminium Shuffler:

There is no such thing as a stalling attitude. A stall is only related to AOA.

How you guess your rate of climb is adequate, with a lower pitch, ignoring now all your take off data?

You are really worried about a TCAS warning during TO due excess closer rate with a target above?

[Capn Bloggs]

How you guess your rate of climb is adequate, with a lower pitch, ignoring now all your take off data?
Come off the grass... at "only" 20° the aeroplane is bettering the required performance by probably 10X! How much extra performance do you want? Even if you only maintained 15°, on two engines, you'd kill any performance issue.

My FCOM limits pitch to 20°; speed is to be allowed to increase if 20° is reached while (trying to) maintaining V2+20.

[Mach E Avelli]

Call me a Luddite, but I treat the flight director the same way I treat most computing devices. If they don't give me what I want - as in 'right bloody now' - I turn the poxy things off, give them a bit of time to review the error of their ways, and then - being the forgiving type that I am - allow them another chance to satisfy my desires.
Somewhere in the recesses of my training I recall reading, or being told, that when the flight director or any other automatic goodie is not giving you what you want, deselect it. It is actually easier to fly attitude and heading than to mentally filter out unwanted information such as excessive pitch up demands or bank angles greater or less than needed to do the job.
As for whether pitch attitude being flown is producing the required climb gradient, surely the old rate of climb over groundspeed formula can be computed mentally by most. All the info you need is right in front of you on the panel (unless you are flying a DC3 with no GPS, and how likely is that?). Or don't pilots do this basic stuff nowadays?

Like Greed, Easy is Good.

[Lord Spandex Masher]

but you don't need to be pushing the aircraft close to its performance capability when light, and you're increasing the chance of triggering TCAS, so why do it when 20o will give all the performance and more than you need?

Why not? You do when you're heavy.

[Capn Bloggs]

C'mon Masher, do you actually know what performance you need to achieve on your departures and how that relates to the actual performance during your greater-than-20° pitch attitude takeoff?

[Denti]

Probably not practical with a low leveling off altitude, but in that case one use CLB 2 anyway, which gives a low climb rate. However in many areas of the world unrestricted climbs are possible and there is nothing wrong with a 5000+fpm climbout. In fact it saves a lot of fuel without any negative sideeffect.

[Lord Spandex Masher]

Bloggsy, of course I do. I also can't see a real reason, and nobody has yet given me one (except some mythical greater than 20 degree made up problems), why I/you/we should be restricting the performance that we've got.

You can recover from that far nose up, but the recovery will be bigger and need more time and potentially more altitude, commodities you may not have just after take off.

Sorry, but that's nonsense. Greater performance means just that whether you're on one or two engines. And having a greater initial climb rate means that you will have MORE altitude. All achieved by this ever so dangerous 21 degrees of pitch.

[RAT 5]

Greater performance means just that whether you're on one or two engines. And having a greater initial climb rate means that you will have MORE altitude. All achieved by this ever so dangerous 21 degrees of pitch.

Given that this apollo rocket type departure is only going to happen up to the flap retraction altitude, which is every airport I've flown a jet into lies between 1000' & 3000' agl., why would you be interested in maximising the initial climb gradient to such an enormous extent for only a few seconds? If you did this out of some places with SID at 3000' and arriving a/c down to 4000' I'd expect to get an RA passing 1000'. It seems like making an relaxed departure into the opposite. Why oh Why?

I think we've reached the time to say "let's agree to disagree." This could keep going round in circles for ever and use up all that potential energy when I'd rather had some kinetic.

[Lord Spandex Masher]

Oh please. Enormous extent! 21 as opposed to 20, really?

Why? I didn't say I do.