Forced Approach Tips

[DaveC]

Hi guys.

I did my flight test a couple days back and partialled due to a botched forced /overshoot. I've done some review with my instructor to relieve some of the issues. I hear that the forced is one of the most failed items on the flight exam, so I'm looking to hear your tips.

Couple of things I have been doing wrong

1. Not trimming properly to keep best glide (60)
2. Not judging distances properly. I keep coming in high, which means i'm fast as well. Not extending my down wind long enough I guess?
3. Slow on the flaps. I know flaps should only be used as soon as you know you've made the field, but if you use flaps too early you wont make the field.
4. Overshoot. Say you have 30 degrees flap down, going 50 KIAS and at 50 feet from the ground, and decide to overshoot. The POH says: Throttle full, carb cold, retract to 20 degrees, airspeed 55 KIAS, and retract flaps slowly. Do you have to retract that first 10 degrees of flap immediately after the application of full throttle and cold carb (wouldn't make sense cause you'd smash into the ground due to loss of lift, no?)
The examiner stressed that it has to be done via the POH procedure (maybe I am misinterpreting it?)

It always seems my forced are hit or miss, but most of the time are too high. Don't think i've been too short once yet, so maybe I just need to get over the thought of being at such a low altitude?

What do you guys think. My re-ride is Monday.

[aileron]

Has your instructor demonstrated the base-to-final figure 8, if not ask. It will help with keeping the chosen field close to a short final while allowing you to lose enough altitude and optimize the timing of deploying your flap.

[200hr Wonder]

Hi guys.

I did my flight test a couple days back and partialled due to a botched forced /overshoot. I've done some review with my instructor to relieve some of the issues. I hear that the forced is one of the most failed items on the flight exam, so I'm looking to hear your tips.

Couple of things I have been doing wrong

Indeed Dave it is the most failed item so don't be discouraged

1. Not trimming properly to keep best glide (60)

You have plenty of time so when the engine quits, nose up and trim for 60, do not do anything else till you are well trimmed at 60. Also you know it is coming so have a field in mind

2. Not judging distances properly. I keep coming in high, which means i'm fast as well. Not extending my down wind long enough I guess?

I have always liked to play this little game: Can I make the far end of the field? Yes, keep going. Keep asking your self that until you no long can make the far end of the field. By the time you turn in and get some flap out you should be good to go. Also as previously stated try the figure 8, this technique works like a charm with a figure 8 approach.

3. Slow on the flaps. I know flaps should only be used as soon as you know you've made the field, but if you use flaps too early you wont make the field.

Not too sure what you mean by that but yes you should only be putting flap out once you are certain of making the field. In a typical 172 the first notch of flaps does not do much to shorten your glide distance but certainly any more than that and the additional drag will start to shorten the distance quite a bit.

4. Overshoot. Say you have 30 degrees flap down, going 50 KIAS and at 50 feet from the ground, and decide to overshoot. The POH says: Throttle full, carb cold, retract to 20 degrees, airspeed 55 KIAS, and retract flaps slowly. Do you have to retract that first 10 degrees of flap immediately after the application of full throttle and cold carb (wouldn't make sense cause you'd smash into the ground due to loss of lift, no?)
The examiner stressed that it has to be done via the POH procedure (maybe I am misinterpreting it?)

Follow what your POH says to the letter. Been a while but IIRC in a 172 the procedure is full power crab heat cold, flaps to 20. Once you have a positive rate and are above the quoted airspeed retract flaps and accelerate away. The danger being at max gross with full flap on a high hot day a 172 will not get a positive rate on the overshoot, so you have to get some of that drag cleaned up or else you will continue to sink.

It always seems my forced are hit or miss, but most of the time are too high. Don't think i've been too short once yet, so maybe I just need to get over the thought of being at such a low altitude?

Well in the real world I would rather touch down 1/2 way down the field and end up in the ditch/trees at 20knots then be short and in the ditch/tress at 55 knots. Just remember that your profile is the same as a power off approach so if you are worried about being short/long go out and do forced approaches to the runway. If you can hit your marks from altitude to touchdown at idle you are good. For the practice flights you are doing do all your approaches power off to the ground. Also if you are high don't be afraid to slip in light trainers they are quite effective at slips.

What do you guys think. My re-ride is Monday.

Best of luck to you!

[cgzro]

Hmm so once you know you are too high are you taking any action or just going along for the ride?

There are lots of things you can do. Even if you have already dumped full flaps and it still is too high.

For example you can make a few shallow s-turns on final.

You can add some extra drag in the form of a slip. Actually you can add a sh**t load of drag in the form of a slip.

And you can deviate from your best glide speed. .. does not make sense does it to overlfy a field at your best glide speed add or drop 5 knots, either way you'll decrease your glide distance a bit.... thats why they call it best anything else is worse. If its gusty add 5, if its nice and calm drop 5.

Open the windows .. add some drag that way...

The other issue is are you recognizing you are high too late? There is a simple procedure you can use to determine where your touchdown point is likely to be and that is to look at a point on the ground and watch it relative to the widscreen. If it moves up in the screen you are not going to make that point, if it moves down in the window you will overshoot it. As soon as you turn final look about 1/3rd down the field and watch what it does relative to the windscreen. Do what you have to to keep it stationary. Avoid flaps until you are on final and you can judge the touchdown point properly .. once you throw the energy away you can't get it back.

There is a good book - stick and rudder that has a good section on forced approaches. Worth reading for its basic common sense but if you practice a lot in the circuit, i.e. pull power on downwind and just fly the rest gliding and use flaps as necessary but not mechanically you will get better very quickly.

[iflyforpie]

I know you probably don't have a ton of flight time to practice before the re-ride, but try and drill into your head how far you can glide from what you see in the cockpit. Can I make this field? that field? etc etc. This is a fixed range of angles below the horizon and change very little.

If you are too high, the best thing you can do is increase track miles. This can be in the form of widening out your turns or doing s turns and bowties. A circular forced approach is by far the simplest (and used by the Space Shuttle for that reason) since all you have to do is increase or decrease rate of turn to keep the field at that golden angle below the horizon.

S turns and bowties are good too, but many people wind up crowding the field and using excessive bank to try and keep turn radius down. All your maneuvering should be to get you to your final key point at a correct altitude for the conditions and from there only minimal maneuvering should be required.


For increasing drag, the side slip is a far better tool than flaps. You can turn slips on and off and change the drag coefficient of your aircraft very quickly without affecting the lift coefficient. Each time you extend and retract the flaps, the plane needs time to figure out where it want's to fly again (hence why we retract in stages). Only use flaps when field is assured.

[DaveC]

Excellent advice guys.

I'm going to try what everyone has suggested. I've been doing most of my approaches with the circuit method. I think the circling or figure 8 method may be easier, so I will give that a go on my solo flight tomorrow morning.

[trampbike]

As cgzro said, practise slips. Your TC examiner might not like it (I have no idea why, but mine did not), but when you are too high, it will save you very often. Of course you should always aim for perfect coordinated maneuvers, but in many cases, a turning slip or a foward slip will help you a lot. In a real life emergency, I don't think I would care too much if my approach would satisfy or not the TC examiner's esthetic tastes. Practise practise practise, and good luck for the re-ride!

@cgzro, reducing your speed to get a steeper descent angle sure seems very reasonable and smart in real life. I was wondering thought if some examiners would not call it a fail or a partial since it's not 100% per the POH. After all, you get a bit closer to the stall by doing this, and it may be considered by some to be a dangerous act and lead to a failure of the maneuver.
Am I just pessimistic about the examiners?

[SuperchargedRS]

X2 on the slips and circle!

Best glide -> DIRECT to landing spot, if your a little high slip, allot high circle.

I can drop a plane faster and at my target airspeed slipping far easier then with flaps.

[dirk82]

In a 172 it says in the POH and in our planes a big sticker on the dash "NO SLIPS WITH FULL FLAP", although everyone still does. Would this lead to a fail on a flight test. I have done it with my instructor and never got slapped but I always wondered if I tried it on the flight test would I loose marks over it.

[200hr Wonder]

Dirk82 re-read the placard, IIRC the exact wording is "Avoid side slips with full flap". It does not say no side slips it says avoid, sort of like the difference between should and shall. In an emergency situation a side slip is acceptable. The reason for the placard is the possibility of a tail plane stall.

[dirk82]

Thanks 200hr, makes sense to me now.

[DaveC]

I found the circle method (circling just prior to the touch down point) to be most effective. Easy to extend or shorten your base by just changing the radius of the turn. Didn't have to use much flap either, slipping took care of most of the excess speed.

I also re-verified the overshoot with my instructor and the examiner and they confirm what you said 200hr (the flaps have to come to 20 immediately).

I'll report on Monday if I passed. Should be OK now though

[Bede]

As cgzro said, practise slips. Your TC examiner might not like it (I have no idea why, but mine did not),

If that is the case, he probably shouldn't be an examiner. Lots of people fly aircraft without flaps and slips are the only way to lose altitude. I always teach students, slid first, than extend flaps once assured of landing. If a student does a forced approach without slipping and barely makes the field, that's not a good thing; you're only one wind gust away from ending up in the trees.

[DaveC]

As cgzro said, practise slips. Your TC examiner might not like it (I have no idea why, but mine did not),

If that is the case, he probably shouldn't be an examiner. Lots of people fly aircraft without flaps and slips are the only way to lose altitude. I always teach students, slid first, than extend flaps once assured of landing. If a student does a forced approach without slipping and barely makes the field, that's not a good thing; you're only one wind gust away from ending up in the trees.

I don't think he hates slips or anything. I used flaps combined with slips, he just didn't like the way I recovered from the overshoot.

[Grantmac]

I am a huge proponent of slipping.
Also of regular use of the power-off approach but that is a different story.

A slip isn't and on-off kind of a deal, it is infinitely variable and can be applied at any point on the approach all the way to the flare. I did a down-hill, down-wind landing yesterday with little weight in the plane and you better believe that the only time I was pointed in a straight line was when the wheels touched.

If you are going to use a slip and you've only got the standard demo on it (I feel they are under taught) then here are a few quick pointers:

-Watch your speed, most people speed-up in the slip.
-Use a little early rather than a lot late.
-If you use a slipping turn it will be wider than a normal turn for a given bank angle.
-Mind your track and correct for drift. Most aircraft can overpower the rudder with the ailerons, so if you need a full slip then use the ailerons to correct.
-If you are going to have to slip to the ground give yourself ample time to arrest the increased vertical speed.

There are probably a few good slip pointers I'm missing so I'll let the experienced folks add their bit.

-Grant

[mike123]

Do you have to retract that first 10 degrees of flap immediately after the application of full throttle and cold carb (wouldn't make sense cause you'd smash into the ground due to loss of lift, no?)

When flaps are extended beyond 20 degrees they produce more drag than lift, so by retracting the flaps from 30 degrees to 20 you are reducing drag and actually helping your aircraft to climb.

[Aviatard]

Dirk82 re-read the placard, IIRC the exact wording is "Avoid side slips with full flap". It does not say no side slips it says avoid, sort of like the difference between should and shall. In an emergency situation a side slip is acceptable. The reason for the placard is the possibility of a tail plane stall.

From 1978 172N POH:

Section 2: Limitations
Placards
Avoid slips with flaps extended.

Section 4: Normal Procedures:
Steep slips should be avoided with flap settings greater than 20 degrees to a
slight tendency for the elevator to oscillate under certain combinations of
airspeed, sideslip angle, and center of gravity loadings.

When landing in a strong crosswind, use the minimum flap setting
required for the field length. If flap settings greater than 20° are used in
sideslips with full rudder deflection, some elevator oscillation may be felt
at normal approach speeds. However, this does not affect control of the
airplane.

Nothing to do with tailpane stall.

[ogc]

I was never really confident wiht my forced approaches until I got into practicing for the CPL flight test and the Power off 180.

It is a great tool to learn, as it really teaches you how to control a glide to a specified point and it lets you follow through to a landing and thus letting you see how you did.

I got to the point where whenever I had open space in front of me in the circuit I would do the power off 180. It was my go to landing for most of my CPL time building.

So my advice for anyone struggling with forced approaches is have an instructor demonstrate this manouver and then practice the hell out of it, then forced approaches should seem easy.

[200hr Wonder]

-Watch your speed, most people speed-up in the slip.

Grant don't forget that when you slip the static port and pitot tube are presented to a relative wind that is not what they are calibrated for so your pitot/static instruments will misread. This depends of course on there position and type of aircraft. What is, however, universally true is that you should not be trusting your Airspeed indicator in a slip. Set your pitch angle, enter the slip and hold onto it. Be very careful not to pitch the nose up and end up slowing the aircraft significantly when you did not intend to.

[Bede]

I read an excerpt from the flight test guide circa 1920. A candidate had to climb to 1500' and shut the engine off and land within 150' of the planned point. You had 7 tries to get 5 successful landings. You also had to demonstrate a figure 8 steep turn and declare that you had done a spin.

http://www.smithsfallsflyingclub.com/tr ... _test.html

[Big Pistons Forever]

I was never really confident wiht my forced approaches until I got into practicing for the CPL flight test and the Power off 180.

It is a great tool to learn, as it really teaches you how to control a glide to a specified point and it lets you follow through to a landing and thus letting you see how you did.

I got to the point where whenever I had open space in front of me in the circuit I would do the power off 180. It was my go to landing for most of my CPL time building.

So my advice for anyone struggling with forced approaches is have an instructor demonstrate this manouver and then practice the hell out of it, then forced approaches should seem easy.

+ 1.

If you are messing up your forced approach it means you cannot accurately asses the actual flght path of the aircraft throughout the manoever. By the time you realise you are too high/low the approach is so bent out of shape that it cannot be salvaged. Practice is the only way to correct this. I would also suggest that when you are practicing completely ignore all the radio calls, checklist reading, passenger brief blah blah blah. Other than clearing the engine, concentrate completely on flying the aircraft. Only when you hitting the field everytime start worrying about the TC flight test bumph, which actually is best perfected sitting in a tied down aircraft while you make engine noises (which of course you don't have to do as soon as the engine "fails" ). Run through all the actions/ speaches/ checklists, touching all the appropriate controls etc untill it is automatic. This cost nothing and is a very effective way to learn

[Grantmac]

-Watch your speed, most people speed-up in the slip.

Grant don't forget that when you slip the static port and pitot tube are presented to a relative wind that is not what they are calibrated for so your pitot/static instruments will misread. This depends of course on there position and type of aircraft. What is, however, universally true is that you should not be trusting your Airspeed indicator in a slip. Set your pitch angle, enter the slip and hold onto it. Be very careful not to pitch the nose up and end up slowing the aircraft significantly when you did not intend to.

In my aircraft the static port is actually a tube inside the fuselage so its still pretty accurate, but I know what you mean.

What I was referencing was the tendency of new flyers to use a point on the windshield or cowling for a pitch reference and not recognizing that when slipping this reference is also false due to the nose being rather far off the horizon in an appearent nose-up attitude.

I like to get trimmed out before a slip and then reference control pressure if the aircraft has good feedback of an off-trim speed. Or if I feel I'm not holding the correct speed (wind illusion or something) then I back off the slip, re-establish my attitude and airspeed then re-enter.

The aircraft I fly has a fairly light wing loading, no flaps, very powerful rudder and a coarse prop. Heavy slips are a way of life if I want to make tight patterns (the only kind in my mind).

-Grant

[appilot]

Since you mentioned that you've practiced the "circuit" procedure, I thought I would mention another trick I was taught for forced landings: if you notice you're still coming in a bit high once you've turned your base, extend it. no, you won't be square but you can bleed off some altitude in the longer leg and slanted final. Could help if you're too high to make the field, but not high enough to circle.
Best of luck!

[DaveC]

Well I passed and got a 4 on the procedure. Thank god for the circle method

[iflyforpie]

In my aircraft the static port is actually a tube inside the fuselage so its still pretty accurate, but I know what you mean.

It will still be slightly inaccurate. The inaccuracy in this case comes from horizontal position error of the pitot tube, similar to the vertical position error we are all familiar with being the difference between Calibrated and Indicated airspeeds.

But if you hold attitude or even just fly with a light touch (not the easiest thing to do when flying a forced), the aircraft will remain at a safe airspeed.



Oh, and congrats Dave!! I know the feeling. I didn't have to do a re-ride (just made the field), but she wanted to see another one just in case....