How do you fly the ILS?

[DB6]

What is your preferred method of flying the ILS? I know there is an interrelation but in principle?

[Mister Geezer]

I was speaking about this yesterday and the general feeling that we agreed on is that if the speed was getting near to or at least 100 knots then 'point and power' would be suitable since if you pitch up to decay the speed then you will be high on the glide - Try flying an ILS at 120 knots in a Warrior or even better fly an ILS in a twin at standard approach speed. I heard a story of a chap who was flying a Cessna 310 and about to enter a hold and he was 40 knots fast so he pitched up in a vain attempt to reduce speed and he gained 400-500 feet … thankfully there was no one above him! However if you flew a Cessna 152 on an ILS at 55 knots then pitching up or down to control speed will not have a significant effect on glideslope deviation therefore elevator can be used to control speed and power can control ROD.

Would be interested to hear what everyone else thinks.

[Chrisdahut1]

aaah the great debate continues.

I've learnt that either way works fine: just pick one way of doing it and stick with it. Personally I use power to control speed in cruise and pitch to control airspeed on an approach. Like mister geezer pointed out, when your operating well on the backside of the power curve, it does help to use pitch to make airspeed adjustments due to the significant amount of induced drag.

[FatFlyer]

With a light plane, you could use power to get the correct descent path for the first part of the ILS as using pitch alone would cause the speed to alter a lot. Obviously , altering one will affect the other, the extra speed caused by pitching down would cause more lift. For the last few huindred feet, pitching for the G/S should only cause small speed alterations and trying to mainitain it with power alone might be too slow to keep on the glide.
With jets, you would probably follow the flight director which maintains the glideslope by pitching and one with low slung engines such as a 737 will pitch a lot as you alter the power making it very difficult to use power as the main way to keep on the glide.
This is just my opinion, I am not claiming to be an expert.

[DFC]

I don't consider flying an ILS to be any different from a visual approach.

The only difference is the cues used to confirm centerline and approach slope.

Thus as I have done since I was a student, Attitude controls airspeed and power controls rate of descent.

What happens when people start IMC training is that there is no revision of the secondary effects of controls including power.

With regard to the pilot unwittingly gaining 400ft trying to slow down for the hold, what is different to slowing down in the circuit?

People who claim to use power to control speed are not adjusting speed in isolation.

To explain, if the aircraft is on the glideslope but a little slow, the pilot increases power and the aircraft accelerates. If the pilot does absolutely nothing else, this extra airspeed will cause an increase in lift and the aircraft will rise above the glide slope.

Thus probably unknowingly, when the pilot increases power to accelerate, they reduce the angle of attack (reduce the attitude) by moving the control colum forward slightly to keep the same amount of lift at the new higher speed.

Power + Attitude = Performance

Works in every situation for me.

Regards,

DFC

[Luke SkyToddler]

Point & power all the way :) The military use it, the big jets use it, I was trained that way from ab initio in the C152 and I've never flown a plane where it hasn't worked just fine.

You can always spot a student that's been taught attitude-for-airspeed when you stick them in the sim on a gusty ILS for the first time and show them their flight path print out, little small deviations all over the place, they don't have a scooby doo about how to really accurately control their flight path on approach. The aircraft goes where you point it as far as I'm concerned and by the way get that goddamn throttle hand working to control that speed!

Particularly when it comes to your classic Piper twin, which is inevitably a draggy and unresponsive mongrel of an aircraft with undersized control surfaces and twitchy throttles (eg the Aztec or Seneca I), a quick blip on the throttle = the same effect as a dirty great yank on the elevator when it comes to airspeed control, and it's about a million times more graceful.

[kabz]

Just from a fairly new IR pilot perspective ...

In a 172, the airplane trims so strongly for a given speed that I just trim for speed whilst level, then reduce power and nose it over to follow the GS down. Then, pretty much I just use power to tweak the descent rate. This is super low workload if you estimate your groundspeed and required RoD, and works really nicely for me.

I've also seen the other side of the argument, which is pitch for ROD and power for speed, and actually done a couple of approaches in a level D sim, which worked out ok. The actual technique was manage the RoD by flying the flight director bars, and just manage the speed with the throttle.

Hmm, not an instructor, so won't pass an opinion :O

[moggie]

Point and power every time.

It is the ONLY technique that works on a jet but it will work on any powered aeroplane - so why use anything else?

If you want to fly level, you do it by setting the correct attitude, so why not do the same if you want to fly a 3º descent? All you have to do is set an atttiude 3º lower than the level flight one and set power for speed.

[Crossunder]

This has got to be THE most worn-out subject on this forum but here we go:
The only thing that will give an increase in altitude (get back on glide slope if below) without a reduction in airspeed is power. You need to add more potential energy to the aircraft. Hence power controls altitude and ROC/ROD. Airspeed is controlled by AoA (CL(pitch control)); you will not find a single aerodynamics text book that states otherwise.
If you have trimed the a/c properly, say, in a descent, and add power, you will INITIALLY accelerate somewhat. But the AoA (CL), for which the a/c is trimmed, wants to remain constant (in the trimmed position) ans as the lift increases you will either slow the descent or enter a climb.
For every AoA there is a corresponding CL, which in turns equals a certain airspeed. Pitch = airspeed. Now, if anyone can find an aerodynamics expert who seems to think otherwise, please let me now. But you won't.

[penltbx2]

Fly the AOA indicator throughout the ILS approach without any other power instruments and then you will know what is controlling. (For those who have an AOA indicator installed.)

[moggie]

Crossunder - theory is fine (in theory, nuclear cold fusion works!) but we are talking practicalities here.

Yes, you can change alttiude by adjusting power - on a prop aeroplane. If you just increase power on a jet without changing other parameters, you will increase IAS first. Then, as the IAS rises, the nose will trim up and you will get a climb - at the expense of you speed control and trim.

However, if you ensure that you hold a steady attitude, adjusting it as required, and then set power to maintain the desired speed, you will have a more stable approach, fewer (and smaller) trim changes and better speed control.

Think about this: You are nicely settled on the ILS, with the speed, power but have failed to get the trim correct. A few moments later you relaise that you have gone low but the IAS has risen. Question: what do you do? Answer no 1: raise the nose a degree ot two and then turn that excess speed into altitude and retrim. Answer no 2: Increase power, allow speed to rise (going lower in the process) and eventually climb back up to glideslope, 20kt fast and needing to reset power, atttiude and trim?

Well, I and the airlines I train for will expect you to raise the nose, turn that excess speed back into altitude and then re-trim to hold it this time.

Think about an autocoupled ILS - the AP flies pitch attitude to correct errors on the glidepath. The AT then adjusts power to take out any error in IAS. If this is good enough for the computer, whey not the pilot? In practice, of course, these two actions occur simultaneously (or nearly so) in just the same way that the pilot should fly the aeroplane.

On aeroplanes with low power to weight ratios, if you have messed up and gone low and slow, then yes, you will need power first to increase the speed to a safe level - but flying the correct technique in the first place this will never happen.

Now, I have made the "point and power" technique work on Cherokees, Bulldogs, Jetstreams, VC10s, Harriers, Tornados, HS125s and B767s. This should be a wide enough spread of aeroplanes to prove the point that the technique is universal!

[Crossunder]

I totally agree with you on that one moggie! But now we are talking about an aircraft that is out of trim ie it is trimmed for a higher speed! And you'll not get that speed correct unless you re-trim for a new AoA = new airspeed.
But hey, I'd also trade kinetic- for potential energy in your example and then re-trim. And as long as you do what works best for you, then what's the problem. I learnt my pitch=airspeed from people who flew MFI-15, Slingsby, Tweet, F-5, F-16, DC-8, 747 and MD-80, so the old "I have flown this and that and it worked for me" isn't proof of validity.
The best thing would, of course be to use an AOA indicator. A constant AoA would mean a constant airspeed, and then use thrust levers to control glideslope. But I don't think we'll ever agree on this, do you? ;)

[DFC]

Why all the 2 dimensional thinking?

The point surely is that we adjust the "performance" to match what is required.

If one is flying a glider down the ILS, one would use attitude to control the speed and accept whatever rate of descent that resulted.

If the glider is too fast, we raise the nose, reduce the rate of descent and thus reduce speed.

If the glider is too slow then the only option available is to lower the attitude to regain speed. That may result in the aircraft descending below the glide slope but withour power, there is nothing we can do to avoid this.

Thus in the glider we have full control over speed but in the absence of power, must accpet the rate of descent that a particular airspeed gives.

That is not the full story........... with reference to the drag curve, we can see that flying at a speed for minimum drag with give us minimum rate of descent. If we fly the approach at say 10Kt above the min drag speed, we now have some adjustment over the rate of descent.

If the aircraft is going high on the glide slope, we lower the nose slightly to add 10 Kt onto the airspeed. This increases the drag and thus our rate of descent increases. Once back on the glideslope, we return to our original performance and slide nicely down the slope.

If the aircraft is going low on the glideslope, we raise the nose slightly to reduce the speed by 10Kt. This reduces the drag and thus with a lower rate of descent we regain the glideslope.

Have I mentioned power yet? No

This is one method of flying the ILS.....accept the speed moving either side of the approach speed by a certain amount.

Now back in a powered aircraft approach at a constant airspeed.....if the speed is right but the aircraft moves above the glide slope.......what is wrong?....answer....the rate of descent is too low......How does one adjust the rate of descent without adjusting the speed.........answer reduce to power.....but remember that in order to retain the speed at the new lower power setting, the attitude must be lowered slightly.

Thus with a stable airspeed, we never adjust power or attitude in isolation.

So to recap, we are adjusting the performance of the aircraft in order to match the performance required to follow the ILS.

Power + Attitude = Performance.

Now no matter what camp one sits in.....power for speed...or power for rate of descent.....it does not matter because in both cases, the pilots are operating the controls in the exact same way to obtain the exact same performance from the aircraft. The only difference is in how they "think" that they are acheiving the result.

Moggie,

If one is nicely settled on the ILS with the speed and power correct, provided that the attitude is correct for the rate of descent then the aircraft will fly down the glide path perfectly.

However, one will have a sore arm if the aircraft is not in trim from constantly pushing or pulling to keep a steady attitude.

Adjust - HOLD - Trim.

The trim does not fly the aircraft.....it simply reduces the control forces. That applies to every type :D

DFC

[DB6]

Interesting results. The reason I posted the poll is that I have to teach RAF students power for RoD and attitude for airspeed and am told that is how it is/was done in the military by ex-Lightning, F2/F3, Phantom, Canberra etc. pilots that I work with.
I learnt the other way (point and power) and find it works better for me so I end up teaching one and flying the other if I don't have a student on board.
But I don't get schizophrenic, do we? No, I don't. We think :}

[witchdoctor]

I fly mine with difficulty (sometimes eyes closed, fingers crossed or uncrossed depending on results!);)

My brother however, teaches his students (RAF K model Herc) power for ROD and pitch for speed control, which is also how I learned to do mine during ATPL training.