Correct use of the Flight Director

[John Citizen]

I am interested in hearing other people's flying techniques, particularly in regards to the flight director.

Are you just supposed to "blindly" follow the Flight Director and do whatever it says (place aircraft symbol in the middle of the cross hairs)

or

Do you set and adjust the aircraft attitude (pitch and bank) by reference to the raw data, using the Flight Director as a guide only ?

[BOAC]

You follow your Ops Manual's instructions - do you have one?

[STBYRUD]

During takeoff and initial climb I find myself often flying my known pitch values and planning ahead with regard to acceleration, climb rate aso. The FDs are naturally only reactionary, they cannot 'look ahead', often they react too slowly and then guide you to overreact to a deviation. On an FD approach though I was tought to fly the FD to the pixel (on our LCDs) while maintaining situational awareness of LOC, GS and speed deviations... Interested to hear more opinions ;)

[John Citizen]

You follow your Ops Manual's instructions - do you have one?

No mention of this subject in our ops manuals :{

[deefer dog]

In that case I would suggest that you first confirm that your PFD is displaying the appropriate FD mode you wish to fly (HDG, ALT, APP etc), and then follow the bars, while at the same time monitoring the raw data.

[BOAC]

Most Ops Manuals I have seen say follow the FD if correctly programmed. Turn it off if you do not follow it or it is presenting incorrect information. There are some situations (take-off rotation, Windshear escape and a few others) where as STBYRUD says the FD will take a finite time to react.

Have you asked your Training Department? They will tell you what to do.

[SNS3Guppy]

The flight director is a useful tool, but know when to follow it, and when to "fly through" it. Remember that the airplane is not the master and you the slave; it's the other way around.

Have you ever had a bad command from the flight director? Ever had one give you a sudden fly-down indication during an approach, or something else that you knew wasn't right, given the data you had before you and your own situational awareness?

The first rule always applies: fly the airplane. Use the flight director, but don't let it think for you. Remember that it's supposed to enhance your awareness, not be your brain. It's there to help you, not control you.

[Tee Emm]

fly the airplane. Use the flight director, but don't let it think for you.

Sound advice indeed. However there is little doubt that generations of airline pilots brought up on FD's are mesmerised by them and lack the confidence to operate without them in sight.

I recall flying a 737 to Guam in the Western Pacific and were radar vectored for an ILS as this was normal procedure for the military ATC. Weather was good with cloud patches on final. The first officer was flying and we had a new to our company but very experienced, former B747 Singapore Airlines captain on the jump seat. The aircraft was the 737-200 with FD 108 FD system. Not a bad FD for straight and level but in those days choice of FD use was left to the pilots. Mostly we never used it for an ILS.

The jump seat chappie was aghast when he realised the F/O was hand flying the raw data ILS and kept on muttering this was bloody dangerous. His whole life seemed to orbit around flight directors and he was genuinely concerned that the company he had just joined didn't use FD's or left it to the captain to decide.

That was over 25 years ago now and his obvious apprehension still stays with me. Having also in a past life conducted a fair bit of simulator training, I see similar scenes where even for visual circuits in the 737 Classic simulator, pilots use the flight director even though on many occasions they don't keep it programmed and one sees needles wandering aimlessly while the pilot rarely looks outside at the runway to check spacing. Others insist on leaving the FD with split cues using the pitch bar to maintain selected circuit altitude.

Raw data flying skills are soon eroded when pilots rely so heavily on FD usage. But that doesn't seem to worry some pilots who seem out of their depth without the FD as a crutch. Sad, really.

[Spendid Cruiser]

FDs are definitely a guide in insofar as one obviously has to be aware of one's flightpath independently of the FD commands!

[PPRuNeUser0190]

In our OPS manual:
F/D on = follow the F/D
otherwise F/D off.

Flying "through" the F/D is not allowed in our company. Either you follow it or you put it off.

[teamilk&sugar]

That's interesting...even on Take-off?

[PPRuNeUser0190]

Sure, with F/D:
you rotate towards the F/D (they are at 15°), once airborne the F/D keeps V2+20.
without F/D:
You also rotate towards 15° pitch and afterwards you adjust the pitch to keep V2+20.

[John Citizen]

How about FD use following an engine failure on take-off ? :confused:

[Spendid Cruiser]

By flying through, I don't think that people here mean doing something different, but not, for example, slavishly pitching up to +20 deg and then having to pitch down to +10 due to the sudden speed drop off, usually then commanding another pitch up as the speed rockets away. One would sensibly see that the FDs are overreacting and maintain smooth inputs to keep the speed stable. Another example would be executing a direct to in a turn with LNAV. One wouldn't just follow the inevitable FD zigzag, but point the aircraft for a sensible intercept and wait for the FD to come in.

What I have seen which I don't agree with, is the PF asking for VNAV an then upon seeing a TCU ahead holding the aircraft at Vx whilst the FD pitch bar descends way down there somewhere. Then I would agree, either select best angle, another mode or switch it off.

[Intruder]

Use your instruments -- that's a PLURAL!

Scan the FD. Scan the other instruments. If they're all OK, then fly the FD. Scan again. If they're still OK, fly the FD; if not, adjust controls and power as needed.

REPEAT CONTINUOUSLY.

[johns7022]

An F/D is nice thing to have, but certainly not a required device in my book...if your leaning on the F/D for all things situational and navigational then it's best you make sure it's on and set up right...or off when not needed so it doesn't confuse you with an erroneous indication.

[40&80]

Scan Scan Scan

[Stanley Eevil]

You can `follow` the fight director and you can `use` the flight director. The two options are not necessarily identical!

[Loose rivets]

I used to dream of flight systems.

We were expected to follow the Zero Reader into a hole in the ground if it told us to. Worked with valves/tubes. As an ex telecoms tekki on valve equipment, nothing would make me follow that primitive pile of rotting rubber and glass anywhere. There just seemed more time to be aware of the total picture with basic ILS.

When finally I flew the Collins FD 108, I really thought it was quite good, but out of workness caused me to finally have the Smiths System catch up with me. Oh, my. I needed a brain transplant to cope with that.

[Microburst2002]

The FD has to be understood as a pitch and bank target indicator.

It tells us which is the pitch and bank that should give us the desired performance.

Then we can achieve those targets either abruptly or smoothly.

FD do not give rate commands, only targets. The rate at which you reach them is yours to decide (within reason). Sometimes, a given target "expires" within seconds and is substituted by another, and you know it in advance so, you wait for the bar to come to you, instead of blindly following it.

Many "fresh" airline pilots tend to rotate too quicky in take off as an instinctive reaction to the pitch bar suddely going up to 15º. Or to bank at too high a rate because the roll bar went fully right after selecting a heading.

When the roll bar "goes" away, I then roll gently until the roll bar comes to me. The thing is more complex when reaching the target heading, though. Then it has some algorithm to resemble a rate command, I deem. If you follow quickly the bar, maybe you undershoot so the bar gives you a small bank for a while. If you are too slow, you will overshoot and the bar will go to the other side. In my airplane, I usually try to use always the same roll rate. Sometimes I note the degrees I turn from the begining till the end of the roll. Then I use that as the lead to go out of the turn and it works very well.

If you look at APs, they take their time to reach FD targets. Sometimes too much!

[Pizza Express]

I think there are lots of people here who fly old generation aircraft like 73s. The A320 family FD is spot on. Rotate to 15 then follow FD.

our company: both on or both off
fd on follow it, not going to follow it fd off.

From what I remember from the 73 days the fds were crap and sluggish. In my opinion the bus fds are way better than the boeing and me as well and I like to keep it nailed.

[STBYRUD]

Someone mentioned earlier that the FDs are pitch and roll target indicators. In the 737 the opposite seems to be the case in my experience, a rate indication seems to be more accurate. They tell you what input you are supposed to make, not what orientation in space the airplane is supposed to be in.

[John Citizen]

Thanks Microburst. This is the type of advice I was looking for.

Sometimes, a given target "expires" within seconds and is substituted by another, and you know it in advance so, you wait for the bar to come to you, instead of blindly following it

How do you know it in advance ? :confused:

When do you follow it and when do you wait for it to come to you ?

I have always blindly followed it but now I am starting to realise that this perhaps not what I should be doing, as it causes me to overcontrol by chasing it :{

[aterpster]

stbyrud:

Someone mentioned earlier that the FDs are pitch and roll target indicators. In the 737 the opposite seems to be the case in my experience, a rate indication seems to be more accurate. They tell you what input you are supposed to make, not what orientation in space the airplane is supposed to be in.

I believe single-cue and dual-cue FDs are different in those respects.

[John Citizen]

If the FD indicates 15 degress nose up and a significant displacement to the right, does this mean :
- you must set 15 degress nose up and bank sharply to the right
or
- you move towards 15 degress nose up (set perhaps 12 degrees nose up) and bank normally to the right and then wait for the FD to move towards you ?

[captjns]

F/Ds of nower days are pretty good for engine failure at rotation. Yes they are pretty good for most regimes of flight too when the MCP is properly set up.

However the cues the F/Ds present are only as good as the information provided them via the symbol generator, FCCs, and navs be they GPS or VHF.

Bottom line the flying pilot must always scan to confirm accurate and reliable information is being presented... situational awareness.

[Capn Bloggs]

If the FD indicates 15 degress nose up and a significant displacement to the right, does this mean :
- you must set 15 degress nose up and bank sharply to the right
or
- you move towards 15 degress nose up (set perhaps 12 degrees nose up) and bank normally to the right and then wait for the FD to move towards you ?
John, you move the controls towards the FD command, the greater the displacement from where you currently are, the more positive you need to be. As you approach the bars, use the controls as required to follow the bars. This may require backing off or slackening your inputs.

I have never flown FDs by saying "it is at 15° Nose Up so that's where I must put the nose". Roll commands are a good example. It doesn't indicate a bank angle as such: there are no bank angle scales in the middle of the AI/PFD. As you roll, the FD bar will appear to come in to meet you, but it's all intuitive and a "just follow it" thing. All the FDs I've flown do not overreact so as long as you are not rough with your handling, there is minimal overshooting. Generally speaking, when hand-flying a LLZ, I find I need to anticipate the FD commands: it's not sensitive enough to "blindly" follow and stay right on the LLZ. It's great with the AP in but not ideal when hand-flying.

My instructor at USAir beat into me: "Follow the Flight Director or turn it off!". Sound advice. Not routinely following the FD is a bad habit to get into IMO. More often than not, it is telling you the right thing, and if one regularly ignores it, say by turning before the PM gets the new heading in, you'll not follow it one day when you should.

[Microburst2002]

Hi John

Pitch
In take off follow SOPs (in A320 15º at an approximately 3º/sec rate, then FD).

It could be stated that flying consists on maintaining a sequence of states of equilibrium. Maintain-change-maintain-change-maintain... all the time. The transition between each two different states is a manoeuver. The transition can occur in many different ways to the same final outcome.

For instance you are descending at 280 kt and 2500 fpm V/S with a given pitch (V/S mode) and thrust (SPEED mode). You ask for "V/S minus 1000" to the PNF. Then the bar goes up. If you lag a couple of seconds, you don't have to rush behind the bar! You are just going to start "late", but there is no hurry. It is not an evasive manoeuvre. You decided yourselve to reduce rate to -1000. It was not the command of God. You will achieve the -1000 when it suits you. No reason to haste. Don´t let the computer push you. Smoothly pitch up. When the rate reaches -1000 fpm, you will have reached the new state of equilibrium. The bar will be in place because you have 1000 fpm. If it moves silightly, the computer has detected a departing trend. Follow it. The computer senses and calculates faster than you. Maintaining a state of equilibrium is not a manoeuver, it is just avoiding to depart from that state with minute inputs.

Instead, you could have pitched up aggresively. The same pitch amount carried out in less time (higher pitch rate) means a higher AoA and therefore a more abrupt and irregular flight path change. Performance will react accordingly. Maybe the computes will determine that it is time to pitch down a bit, now, so you find yourselve pitching down so as to not go below the -1000 fpm performance target.

I would say that, as a rule, a good manoeuvre is such that you transition progresively from the original to the final state as if you were passing through infinite mid states. Like a "quasistatic" change. It is much better for those pilots who still have to trim, specially.

FD "gains" and algorithms are designed in a given way. I don't know which way:confused:. But in a specific way. If you follow the bar in the way you are expected to follow it by the designers, then it will work very well!
But who knows that way?

In Roll:
Same applies to rolling into a turn. The bar moves instantly. If the change of heading will be large, the FD will command maximum bank. You roll smoothly to that bank. You will know what the commanded bank is because the bar is in place.

In the case capturing a heading or a track or a course: the FD bar has some mathematical algorithms that depend on the bank angle, the heading rate of change, the altitude and others to determine when to start rolling out of the turn. The more you lag after the FD bar moves, the more agressive you will have to be to avoid overshooting. I deem that after the FD bar moves you still have a second or so to start a smooth roll rate out of the turn without overshooting.


My advise:
Follow the bars or turn the FD off, but don't haste in doing so. Fly as smoothly as you would if you were flying FDs OFF. Once you have the bars in place, don't let them go. They are there to help you maintain the demanded performance without you having to use too much brain resources. The FD is a wonderful tool, specially in approach.
With practice you can fly it perfectly (and not be flown by it). Practice means not only that you have to fly AP OFF regularly... But also with FDs OFF, if they let you. And even without A/THR, if your airline or captain are not scared of that :eek:. Only then you will really master flying with the FD.

Hope it helps

[latetonite]

You stick to that modern FD. It even guides the A/P how to autoland. Usually a better job than the pilot. For most pilots it is a bit like playing tennis: discussing which expensive racket while going for their first tennis lesson.

[aterpster]

latetonight:
You stick to that modern FD. It even guides the A/P how to autoland.

In most modern installations both the autopilot and the FD are controlled by the flight control computer (FCC or whatever name an OEM chooses to call it). So, when the auto-flight is not engaged, the FD shows you what inputs will be provided to the auto-flight if engaged. When, auto-flight is engaged then the FD is simply a monitor of auto-flight track.

So, for any mode, including autoland, it's the FCC that is really in charge of the computation for the FD and the autoland maneuver.

[d105]

How do you know it in advance ?

When do you follow it and when do you wait for it to come to you ?

I have always blindly followed it but now I am starting to realise that this perhaps not what I should be doing, as it causes me to overcontrol by chasing it

On the 738 a few quick examples come to mind.

1. After take-off the FMC provides TO/GA thrust until thrust reduction altitude. Thereafter it goes into N1 mode which usually means a couple of percentage points thrust drop. If you follow the FD during take-off it will take you up all the way to the pitch which holds V2+15. After the drop in thrust, you need to pitch down up to 2° to maintain V2+15 with reduced thrust. Instead of blindly following the FD you pitch for V2+15 at N1 thrust instead. No pitch reduction required and a smoother ride follows.

2. In Europe we usually fly 250KIAS below FL100, as per ICAO airspace classification limits. Above FL100 the FMC commands ECON climb speeds (ranging from 280 tot 320KIAS). the FD will command a pitch of roughly 3° tot 4° to accelerate. This is much too low. When the aircraft reaches ECON speed it needs to pull the nose back up to 5° to 6°. At 310KIAS you can feel that pull in the tail quite a bit. Instead of follow the FD you pitch for 6° at FL100 and let the aircraft slow accelerate to ECON speed. No pitch change required and again a smoother ride for your passengers.

3. The turn to final from an outbound leg of a procedure turn is calculated at constant bank angle from the limiting point of the outbound leg to the final. This can lead to the FMC commanding a turn of 10° or less, which is just ridiculous. Instead you fly through the FD to 30° bank and intercept the final by the shortest route possible. Thereby helping ATC, reducing fuel burn and speeding up your operation. The FD will follow once you are on the inbound course.

The list goes on basically. If you fly the aircraft precisely on the FD your pax in the tail will feel it. The FD is much too jerky, reactionary in nature and in general causes pilot induced oscillation.

The FD is a safeguard, not a "point at me and stop thinking" tool.

[Ocean Person]

The best thing about a Flight Director is the switch that turns it off. I've never encountered a positive FD that really earns its keep as they all seem to arrive late. They clutter up the main picture, degrade positive attitude holding and contribute nothing towards good scanning. Best described as something of a pest. The runway symbol is far more important.

[A37575]

and contribute nothing towards good scanning.

But then you get the counter argument that instrument scanning is not important any more because you simply follow the magic FD and magenta line and that relieves you of the traumatic stress of scanning:mad: