Holding Altitude

[Tero]

I have a skills test coming up soon and would appreciate some advice and/or tips on holding altitude accurately. I have found this to be the most difficult aspect of flying since starting training.

When flying in turbulence it gets even worse and my altitude can vary by several hundred feet. In controlled airspace I have to make a conscious effort to monitor the altimeter and VSI on a regular basis to avoid infringements.

I believe I'm trimming effectively so is this just a learning curve and is likely to be a show stopper in the skills test?

[Captain Smithy]

I think we've all come across this at some point. I know I have!

Usually when the aircraft is hunting in vertical speed, that is a sign that the aircraft is incorrectly trimmed. You may think you have trimmed it out OK, but it won't be.

Check the obvious things. Is the attitude right? Make reference to the horizon using the top of the instrument panel in S&L flight. How high above the top of the panel should the horizon be? Is the attitude correct? That's the first thing.

Secondly, the airspeed. If you've trimmed out for 90Kts but after hitting a thermal you've slowed to 85Kt or accelerated to 95Kt, then the the aircraft is no longer in trim. If you're hunting in airspeed then that's a sign you are incorrectly trimmed.

Third, check the power setting. Do you have normal cruise power set? Is the carb heat on? Have you adjusted the mixture?

I was always taught PAT: Power, Attitude, Trim. When you trim you are trimming for a certain attitude at a particular airspeed and a set power setting. If one changes then it's back to square one and you'll need to re-trim!

Hope this helps. Some PPRuNE-dwelling instructors may care to elaborate? (Apologies if my attempt at explaining is mince; perhaps some FI patter may help!)

Smithy

[Molesworth 1]

If you are flying VFR and controlled airspace is not an issue and you are out of the circuit then it is not necessary to keep a constant altitude. If you have trimmed correctly and you gain or loose height due to turbulence don't worry about it - the aircraft will settle itself again after a while, as long as you are not constantly chasing the airspeed or the altitude.

On the other hand, if you are in a situation where you do need to keep a constant height, then adjust your height immediately. Don't wait. Be careful not to over-correct.

[Whopity]

and would appreciate some advice and/or tips on holding altitude accuratelyStart with the basics, a correct scan LAI; Lookout (wing tip to wing tip) pause in the middle, and check the Attitude (pitch and wings level) then briefly check the Instruments (Altimeter and Ball). If you spot an error adjust the attitude and balance before continuing the scan.

It takes quite a while to regain altitude which tells you that it also takes quite a while to deviate from it, so you are not picking it up and acting on it soon enough.

[Tero]

so you are not picking it up and acting on it soon enough.

This makes sense. In retrospect I spent the first few hours fixating on the instruments with my instructor imploring me to look outside. Maybe I've turned full circle and need to incorporate an instrument scan on a more frequent basis.

I'll need to practise this a bit more as the skills test is August 4th and I believe the tolerance is 100 feet or so - this is the bit that worries me.

[Big Pistons Forever]

As was pointed out earlier trim is secret to holding a constant altitude. But before you trim the aircraft has to be in equalibrium, that is not climbing or descending (level flight attitude) and at the right airspeed (correct power setting). I find many new pilots rush the trim and never really get the airplane properly trimmed so they end up chasing the altitude because the aircraft will climb or descend as soon as the pilot becomes occupied with any other flying duty. With respect to Molesworth 1's comment about holding altitude not beeing important....I could not disagree more. Holding altitude is like every other flying skill, you get better with practice. If you make an effort to fly accurate altitudes you will quickly find it becomes easier and easier.

[BackPacker]

Best test to see if you've trimmed properly: Let go of the stick/yoke. Not just for a few seconds, but for five minutes or so. Watch the altimeter for any trends and trim in tiny, tiny increments, then watch the trend again. At the same time, small bank excursions can be corrected with the rudder. But try to keep your hands off the stick/yoke the whole time.

It will not work in turbulence and it's also a bit too coarse a method to apply in controlled airspace, but it's a very good training exercise. If you have height excursions several 100 feet up or down it's not just turbulence or not paying attention, it's also overcorrecting and improper trimming.

The other thing that you might be doing wrong is leveling off after the climb. Interesting piece about this in last months Flyer magazine. After leveling off, maintain full power and let the aircraft accelerate to cruise speed (assuming cruise speed is below redline RPM). Only then select cruise RPM, and trim. If you set cruise RPM immediately after leveling off, but while the aircraft is still accelerating, you'll be hunting the correct power setting and trim for a long time.

[IO540]

Trim, trim, trim :) Should be taught in the PPL but often isn't.

But to be fair, it is hard to hold altitude if flying in turbulence. It's hard work, and vertical excursions are accepted - so long as you are not flying 100ft below the base of CAS :)

In VFR, OCAS, altitude is not important legally, but one should aim to fly accurately in general. Then, when progressing to instrument flight, it becomes a lot easier.

[FREDAcheck]

I agree that one should certainly try to keep within +/- 100 feet. However, I also agree that it's not always easy. Today there was no significant turbulence, but flying at around 3000 feet below broken cloud at around 6000 feet, I had to watch the altitude all the time. I'd get it perfectly trimmed at normal power and speed and it would be alright for 30 seconds, then the altitude would start to drift up or down. I'd probably flown into slightly warmer or cooler air, or into a slight up-draft or down-draft, and now it was out of trim. I had to keep re-trimming. And that wasn't in any perceptible turbulence.

So to say:
Usually when the aircraft is hunting in vertical speed, that is a sign that the aircraft is incorrectly trimmed.
is true, but it may have been correctly trimmed a few seconds ago!

[Tinstaafl]

As others have said, trimming properly is one of the key skills to accurate - and relatively workload free - flying. Lots of pilots try to finalize the trim setting before the aircraft has stabilised. Fair enough to wind in some trim to relieve the control pressure while it is still accelerating but don't confuse this with a final trim setting. The aircraft must have stabilised at a constant speed with power set before a final trim can be done.

Assuming your scan to monitor performance is OK, how tightly are you holding on to the control column? Your grip affects your ability to trim to 'hands off' - the tighter you grip the less you're able to feel whether you're still holding pressure on the control column. The goal is to hold the column like a lightly gripped pencil. Even better if you can hold your forefinger & thumb far enough apart so that only one of them can be in contact with the column at any time. Try using a grip with your 2nd, 3rd & 4th fingers tucked into your palm, leaving only your 1st finger & thumb to grip the column - then spread those digits far enough apart so that they can't both touch the column at the same time. You'll soon see if you're having to push or pull on the column to hold an attitude. Thumb to push, 1st finger to pull and avoid squeezing the column between them.

At times you will need more pressure on the column than either of those two digits can provide, so use more fingers to pull, or the heel of your thumb/palm of your hand to push. Return to a single digit pushing or pulling as soon as trim state allows. Remember not to squeeze though.

[Johnm]

Power, Attitude, Trim

That's correct for levelling off after a descent

After a climb it's Attitude, Power, Trim or you'll never settle it into a reasonable cruise

[Lightning6]

Power, attitude, trim....Fine, but you have to settle your power and attitude first, all to easy to 'hunt' the power and attitude, i.e you increase power, or decrease power and attitude before you allow it to stabilise, once stabilised, trim to maintain. If in turbulence, then just adjust as necessary using the stick (or yoke), if it's heavy turbulence, let it ride, just keep your wings level and watch your airspeed.

[ExSp33db1rd]

PAT Power, Attitude, Trim. as has been said, for everything i.e. starting a descent, levelling off after a descent, starting a climb EXCEPT levelling off after a climb, when it's APT.

Think about how you would use the power ( accelerator ) in a car to maintain a constant road speed up and down a series of hills.

Do nothing in a hurry, make a small change and wait, don't 'chase' airspeed or height - get the attitude right.

Find a rivet, or corner of the windscreen, that matches the horizon in a turn, and look ahead of the nose in the direction of turn, but out of the corner of your eye see the rivet you have picked and pull it towards where your eyes are looking - couse, you'll need a different rivet - or whatever - for left and right turns ! Relax your iron grip on the control column.

[Captain Smithy]

Oops, got it the wrong way round, silly Smithy! Thanks for correcting me.

Always proofread post before posting! Lesson learned.

Smithy :\

[BackPacker]

I'd probably flown into slightly warmer or cooler air, or into a slight up-draft or down-draft, and now it was out of trim. I had to keep re-trimming.

Actually this is one of the situations where, arguably, you should NOT re-trim.

Trim, in a light aircraft, essentially determines the speed. The power setting determines whether you go up or down, or stay level, with that speed. That's simply the way the balance of forces works out.

When you enter an up- or downdraft the balance of forces is still the same so you're technically still "in trim", but you're just climbing with the air, or descending with it. If you want to prevent that, adjust power a bit and use the stick to help the aircraft settle a bit earlier in its new attitude, or use the stick to force the aircraft to climb or descend without changing power and accept a speed variation.

Retrimming in this situation should not be necessary, assuming the up- and downdrafts are temporary. Because once you exit the up- or downdrafts you'd otherwise have to trim again for a stable cruise.

And that's the whole idea about trim: you trim for the stable situation. The stable climb, the stable cruise or the stable descent. Anything temporarily is handled by accepting some stick forces without retrimming. You also don't trim while making a turn, do you?

Having said that, chasing the correct altitude, attitude and airspeed in turbulence can be really tiring and uncomfortable. If you're in controlled airspace and have an altitude assigned, or near controlled airspace and worried about descending through the base, or something like that, you have no choice. But if you're out there in the blue wild yonder it is far less stressful, and more comfortable for your passengers, just to accept the occasional altitude excursion as long as it's not too severe. In the end the up- and downdrafts will probably cancel each other out anyway.

[FREDAcheck]

Retrimming in this situation should not be necessary, assuming the up- and downdrafts are temporary. Because once you exit the up- or downdrafts you'd otherwise have to trim again for a stable cruise.Agreed; it's a matter of judgement as to what constitutes a temporary change.
But if you're out there in the blue wild yonder it is far less stressful, and more comfortable for your passengers, just to accept the occasional altitude excursion as long as it's not too severe. In the end the up- and downdrafts will probably cancel each other out anyway.Again, I agree with that. However, even out of CAS if you're getting a Traffic Service then from memory I think they expect you to stay at the level you've told them (unless you've told them you're manoeuvring), so they know what to warn you/others about. At any rate, I try to stay within +/-100 feet.

[Lightning6]

Tero...Plenty of good advice above, just to say that if you are in CAS, you should advise the controller that you are in turbulent conditions, But, if you're taking your skills test, I doubt you will experience anything other than mild turbulence, in which case forget trim because it's useless in such conditions, just fly the plane using stick(yoke) to maintain altitude, as has been said before, small inputs, you don't want to overstress the airframe, just keep it as close as you can to maintain approximate altitude, but above all, keep an eye on your airspeed, I don't think you will experience anything as medium or severe turbulence on a skills test, but worth bearing in mind for the future.

Good luck with your skills test.

P.S. As FREDAcheck says, you should be able, in mild turbulence, you should be able to keep within +/- 100 ft, forget the trim, just fly the plane.

[Pace]

Do not keep retrimming. Set the trim for a given power speed. Doing it even in turbulence becomes second nature.

It maybe worth watching what happens when you have the aircraft on autopilot with alt hold in moving air.

Watch the VSI and the ASI ON on autopilot. You will notice as you hit rising air the VSI will indicate a slight climb. The aircraft will compensate by trying to hold altitude by pitch forward. As it does so the speed increases on the ASI which further increases the desire for the aircraft to climb.

Watch what happens in sinking air. The VSI indicates that sink! the auto tries to hold altitude with the result that the aircraft pitches up and the airspeed declines. ETC ETC ETC.

You could not possibly be trimming for every movement in the air flying manually so trim it for still air and then command the aircraft to hold altitude with small amounts of pressure on the control column.

Scan out of the aircraft but also watch for trends on the VSI the altimeter and the ASI.

If the VSI starts to show a trend followed by a movement up on the Altimeter command the aircraft back onto the altitude and hold it there. It is a matter of slight pressure on the column if you have the aircraft trimmed correctly for still air.

Pace

[Tero]

Thanks for all the good advice and encouragement. The skills test is next Tuesday and the weekend will be spent doing some revision with my instructor. I'll post the (hopefully positive) result next week.

Tero

[Lightning6]

Good luck Tero...I shall look forward to your positive post next Tuesday. :ok:

[RTN11]

On my CPL it finally sunk in that it's well worth taking all the time you need to trim correctly, so you then don't have to make any adjustment for the remainder of your nav leg.

Even if it take 3-5 mins to get it set correctly, it's well worth it.

1) Select the attitude for level flight.
2) Hold that attitude - don't trim right away, just hold the force on the stick
3) CHECK - am I climbing or descending?
4) adjust as required, still holding on the stick. If you have adjusted, return to step 2.
5) trim very accurately.

Once you have the aircraft trimmed, the height really shouldn't vary by more than +/- 100' and you can easily return to your referance altitude as stated, by either easing the stick and accepting a brief speed change, or a slight adjustment of power. Once you are set back to your straight and level power/speed, you will be back in trim as you set before.

Make sure you follow the steps correctly, Don't trim as you alter the attitude, or you will be chasing the VSI for the whole nav leg, and then everything falls apart.

[kevmusic]

Tero, I'm at the same stage as you. Today I had a mock skills test which would have been a fail; mostly because of navigation errors but also with poor level-keeping. It was a very thermic day today and like you, I was popping up and down like a yo-yo, by 2-300 feet either way! :uhoh:

Good luck on Tuesday, and may your airmasses be stable. :ok:

[B2N2]

What airplane are you flying and is there slack in the trim system?
Back in the good ol' days used to fly an Arrow which was impossible to fly within a 100 feet of altitude due to play in the trim system.
It may not all be pilot error....:ok:

[Lightning6]

If you are trimmed ok in calm air LEAVE IT, keep an eye on your VSI and ASI and 'Seat of the pants', correct straight away (using the stick/yoke) to maintain altitude and airspeed whilst keeping the wings level.... but to not lose too much altitude:-

1..Seat of the pants..you can feel whether you are going up or down.

2..Adjust accordingly checking your VSI and ASI ASAP

3..Forget about him/her in the RH seat, just fly the plane as if you were on your own.

4.. If you are in moderate to severe (unlikely) your examiner should take this into account.

[Tero]

What airplane are you flying and is there slack in the trim system?

Most of my flying was on the PA38. Now flying a PA 28 which is easier to trim. I flew with my instructor yesterday, did some VOR tracking west of Brussels followed by steep turns and then some circuits and a panel exercise at Charleroi. Throughout the flight I was making a conscious effort to focus on power, attitude, trim and to incorporate an instrument scan at regular intervals. It was certainly better - not perfect - but I was staying within 100 feet of target altitude most of the time.

The plan is to fly a range of exercises today and tomorrow as revision before the test which is 3pm on Tuesday. I'm also thinking it might be a good idea to get a some circuits in a few hours before the test just to stay sharp. I'll post each day with an update.

Tero

[Tero]

After a tiring few days of intensive practise I took the skills test yesterday and passed. I flew about six hours on Sunday and Monday with my instructor going over a range of exercises in preparation for the test and this strategy really paid off as I was in an aviation mindset by the time Tuesday came around.

In the morning I flew some solo circuits practising landings with various flap settings and speeds and then sat down to plan the Nav which the examiner had given to me the evening before. Once the planning was done it was then on to Mass and balance calculations, checking weather and notams etc. When the examiner arrived he reviewed my preparation and my documents then asked me some questions on the aircraft.

Weather was perfect with 26 degrees, blue sky and excellent visibility. Engine start, taxi and run up went without a hitch once we managed to offload the wasp buzzing around the cockpit who seemed determined to hitch a free ride. We started with some normal then precautionary circuits before moving on to a panel exercise overhead the field at 2500 feet. So far so good. We then flew to an area just south of Brussels to do some steep turns, stalls and unusual attitude recovery. In my opinion my performance was not as good as I would have liked. I completed the exercises correctly but just felt it was not as smooth as I had done before.

There was no time to dwell on this as he immediately directed me to Feluy to start the Nav. First leg was tracking the Affligem VOR for 22 miles making sure to stay below Brussels TMA. Overhead the VOR we turned west to Amougies which is a very small grass field and difficult to find. My track keeping was good until the end when I allowed the aircraft to veer off course as I was looking for the field. I could not see it and started to get worried until my examiner pointed out that it was directly below us - doh!.

Then south to find a road intersection at Peruwelz near the French border. This route follows a narrow corridor between Chievres AB CTR and Lille TMA but I found it easily. Then back to Charleroi with an entry point at Thuin, but a direct route would go too close Chievres and enter EBCI CTR before reaching Thuin. So I had planned a leg which would take me to a point over a wooded area just south west of the CTR and then a timed 1 minute leg before turning east to find Thuin.

On the way however we diverted to St Ghislain where we made a low approach. There was a feeling of relief when Thuin loomed on the horizon and ATC cleared us to join the downwind. Shut down 2 hours and 24 mins after start and the silence in the cockpit was deafening until the examiner turned to me and said 'lets go and get your paperwork in order so that you can get your license'.

At the debrief he pointed out some of my errors and items I need to work on with very constructive advice on how to avoid them. Next step is to tackle the paperwork mountain with the lovely people in Federal mobilite et transport and actually get the piece of paper after which I intend to have some fun flying some trips for the remainder of the summer. Then an aero course is something I would like to do just to experience the difference.

[BackPacker]

Congratulations. Well done. Sounds like a grueling exam. Mine seemed to be much easier.

[Tinstaafl]

Well done!

[Ryan5252]

Thats great news! Very interesting to read how your flight went - not sure I would have done so well with a wasp in cockpit at the start!!
My day will come one day but thats a long way off for now but well done to you :D