TnG Danger ? How far to let a student go ?

[kabz]

Here's a question for flight instructors :

The student made a longish landing on a tng and you've prompted them to look ahead to the 100' treeline obstruction. The student takes the hint (trees!!! arrrgghhh!!) and closes carb heat and quickly opens the throttle and climbs steadily at 45 kts at full throttle, apparently without noticing that full flaps are still out.

How far do you let them go ??

What might happen ?

What if the student is smart and can work out afterwards what might have happened ?


(If anyone asks, I'll post what happened to me.)

[Speedbird252]

When you say that he`s touched down and then closes the carb heat, are you implying that he touched down with it still set to hot?

I hope not! He might not make it even with his flaps up!

[kabz]

I thought the 'n' in TnG was :

flaps up
carb heat cold (on since landing check/power)
full power

That's not the real point though. The question is what should happen if the student leaves the flaps down and takes off. How long do you let them continue before prompting them into a go-around style cleanup...

i.e.
first notch of flaps up
look for increasing speed w/ positive climb
etc.

[2Donkeys]

The Carb Heat question is one of those old faithfuls that come round from time to time.

The Flight Manuals for certain trainers insist on Carb Heat being left on until touchdown. For other popular makes, the advice is strictly to select cold on short finals.

Those faithful trainers of olden times, the Chipmunks, have the Carb Heat permanently wire-locked hot when on the civilian register.

There is no overriding correct answer.

To the original question, you allow the student to continue for as long as is reasonable without endangering the aircraft. There is no general answer to when that point is reached either. This is down to your nerve and your professional judgment. What is acceptable on a cold day with a small female student is utterly inappropriate on a hot July day with a 20 stone student(like so many other things in life :))

I suppose the motto is "Know your aircraft"

-2Donkeys


[This message has been edited by 2Donkeys (edited 04 April 2001).]

[Multp]

2Donks:
Just a small point, but in the RAF Chipmunks the carb heat control was wire-locked in the hot position. The RN (and possibly the Army too)used the cold air option. Going from hot to cold on the runway involved a hand-change on the stick.
I've instructed on a variety of light aircraft with Lycoming engines and believe the best option is cold air at about 300ft on final approach...makes quite a difference in some models of the C150 if 40 flap is being used for the approach...you may even go up after applying power and before getting flaps back to the take-off position.
As to kabz question, agree that it depends on the instructor and the student. But once the teacxhing/learning point has been made, there's little need for the instructor to sit there as the student's 'thinks-bubble' and stress level grow. The instructor should either prompt and encourage or take control to sort the aircraft out and whilst doing so debrief the student.
Poor old kabz, seems like you've had few unfortunate experiences!

[Checkboard]

Let them go long enough so that they can't use the "Oh, I was just about to do that" justification. Say 10 seconds of climb or so, provided that the aircraft isn't under threat. After that there is no training benefit in letting the situation continue.

Wait any longer and you run the risk of being distracted by something else yourself, and not getting around to correcting the situation until embarrassingly late. (OK, maybe not with a full flap climb, but with other less-obvious errors.)

[Ivan Ivanovich]

Carb heat on Finals?

It depends on aircraft type, of course. Each aircraft displays different levels of susceptibility to carb icing. However, at what throttle setting is carb ice most likely? Therefore at which phase of flight can we most reasonably expect icing to occur? And when can carb icing leave us with so little time to react? On approach.

Furthermore, a couple of hundred rpm less on a go around will make little difference for the few moments it takes to close it should a go around occur. I always try to instill a automatic reaction of carb heat cold action when full throttle is applied. Start this earlier enough and the student will never forget to close it when he or she selects full power. Works all the time and covers all eventualities.

If it does fail, they'll still climb away safely, unless you're in Joburg in Summer!

[kabz]

Well, call me dumb, but at 300 feet with full flaps in a 172, the airspeed wasn't much better than 40, way down near the bottom of the white arc. It was my dumb fault for not cleaning up, but there's enough that can go wrong and kill you at that point, that I think myself, the instructor and the airplan were all in some danger of stalling and spinning in.

Just a stray gust might have been enough. Or my right foot getting tired and coming off the rudder...


There's a great description of something like this from this link.

http://www.monmouth.com/~jsd/how/htm/snaps.html
============================================
One fine spring day I was instructing a student who had about 5 hours experience. This was her first lesson in slow flight, but she was doing really well: she was maintaining the assigned altitude, the assigned heading, and the assigned airspeed (a couple of knots above the stalling speed). She was also doing a good job of keeping the inclinometer ball in the center, which required considerable pressure on the right rudder pedal because of the high power and low airspeed. I was really enjoying the flight, but suddenly I developed a feeling that there was something wrong. Gradually it dawned on me what the problem was. The problem was that the airplane was upside down.

Here's what had happened: her right foot had gotten tired, so she just removed it from the pedal — all at once. This produced a sudden yaw to the left. Naturally the left wing dropped, so she applied full right aileron. The nose was dropping, too, so she pulled back sharply on the yoke. The next thing anybody knew, we were upside down.

I took the controls and rolled the plane right-side-up. We lost about 500 feet of altitude during the maneuver. The student asked "What was THAT?'' and I said "That was a pretty nice snap roll''.
============================================

[Luftwaffle]

Not nearly as interesting as inverted slow flight, but I have another way of using the carb heat on a touch and go. At the flying school I instruct for now, in Cessnas, on a touch and go it's flaps up, full power, carb heat off. The theory being that it's ALWAYS power before carb heat, in a missed approach, or a stall recovery and they don't want to teach a different order for the t'n'g.

My rule is to let the student go as far as I am confident that I can safely recover the aircraft from the NEXT unexpected thing they could do. For me, that's not very far. I'd probably select flaps up myself, saying FLAPS *UP*! as soon as it the student pushed in the power.



[This message has been edited by Luftwaffle (edited 07 April 2001).]

[Tinstaafl]

A couple of contributors have mentioned selecting flap prior to power to commence a go-round. I think that's incorrect.

All manuals for light a/c I've flown specify full power application prior to flap selection. More correctly, damned if I can remember any manual that specified flap selection first.

The goal is to change the a/c flight path from a descent to a climb ie to increase the potential energy stored by the a/c. It's the application of power that causes this. The sooner more energy is added to the system the sooner a gain in height will be realised.

All the rest eg carby heat on/off, flap selection, gear selection etc, enable more efficient use of the applied power however none of them - either alone or in combination - will cause the aircraft to gain height.

[Ivan Ivanovich]

I've never come across any procedure where flaps are taken up first; it doesn't make sense! Whilst you're pulling up your flaps, you're still going down. Don't forget you're only going to get rid of drag flap first anyway. Yeah, get the power on, you'll still climb in most light singles with full flap and full power, but you won't climb with no power!

You'll also climb with full flap and carb heat selected - and it also takes a while for the heat in those cylinders to be irreversibly affected by all that extra heat. Chances are you'll be back on the approach before the engine realises that it's getting a little hotter, anyway.

In short: get the power on - try to instill automatic carb cold select at this action, then clean up the aeroplane.

[YouNeverStopLearning]

Every light A/C I have flown, and with respect to the FTO's ops manual, requires Carb Heat to HOT for descents. This includes the approach.
Then Carb Heat to COLD on short finals during the short finals checks in case of a go around. I think that on the CFS course this is part of the C.R.A.P.P. checks.

Going around:
FULL power smoothly whilst checking carb heat is cold, followed immediatly by removing the final-or-drag flap if it is in use.
When assured of positive ROC and airspeed SAFE and increasing towards normal climb speed, flaps retracted ONE STAGE AT A TIME.

So by the time you are raising the last stage of flap you should be well away from the ground and with safe A/S incase your type experiences any sink during the retraction of the last stage of flap, which is usually an all-lift setting.

Remember that when you retract flap you lose any lift you had from it IMMEDIATLY, but you still have to WAIT for the A/C to accelerate.
Even when you remove the drag flap you have to wait for the A/C to accelerate.

On the subject of when to intervene, you should do so when you believe that the safety of the A/C is about to be endangered, or if this isn't the issue, after more than long enough for the student to have spotted the problem, given their stage in training and ability and tiredess and experince, etc.........

[chicken6]

Every now and again I read something on here and that same day go out and fly what is being discussed. Here is yesterdays story.

Was doing a C172 type rating for one of my recent PPL graduates and in the circuit doing TnGs. Not used to floating quite so far, and not flying by feel yet, still using threshold speeds by numbers on the ASI for reference (i.e. flying 5-8kts too fast). I made him keep pulling back and not let it touch the ground as far as possible (400m later, we did). OK, we've landed.

Away we go, he put full power and CH cold in the same movement but he didn't retract the flap so I did and said, "I've got the flap then if you haven't" to which he replied "Oh sorry I'm a bit busy". He actually was busy because I had been talking him through the flare, so I didn't mind unloading him for a bit.

Next circuit, he does the landing all by himself (still not stalling fully, but mains first), his touch'n'go so full power and CH cold, didn't retract the flap. Up we go, S+L attitude but 60kts and +500ft/min. He figured out at 200' that all was not well, cleaned it up in one stage (which I left) and juggled it very nicely to keep climbing and smoothly transitioned to the normal climb.

Why did I let so much go on the second one?

1. Density altitude was -280'
2. Only two POB, 100L
3. 160hp, limited to 30deg flap.
4. I wanted to see how it went! And it was actually climbing so I had no complaints. Also having read this thread first I picked up a good point from Luftwaffle - ready yourself for the next bad thing they could do and if you don't think you can handle that dont' let it get there. In this case the worst thing he could have done was let go the c/c and we would have pitched up on the way to a stall/spin accident. In preparation for this I had my hand ready to push forward.

Essentially I let it go and told him about what happens when it's hot, when it's heavy. When we fly at MAUW he will get a better appreciation for the increased radius of turn, and find out what increased stall speed actually means for the operation of the a/c.



------------------
Confident, cocky, lazy, dead.

[Fuzzybear]

I think there may have been a little confusion along the way between TnG and Go Around.

A TnG is a landing followed by a take-off. Touch and gos are of little benefit to very early students particularly if the runway is short. A landing enables the student time to think before the next circuit.

If you are intending to TnG the accepted routine is:
Flaps to Take-Off after a successful landing
THEN Full Power
(When the carb heat is put to cold is not critical, but of course to develop full power the carb heat must be cold)

Get into a habit of only applying power once the flap has been raised, if there is insufficient runway remaining STOP! Some would argue that the flaps should have travlled to the take-off setting before the power is added if they are electric as in the C172.

The runway length and any obstacles are important when desciding how badly wrong you can let the student get it.

If the student does go around or omits to retract the flap on the runway, the power is obviously the only thing which is helping you go up! YouNeverStopLearning covered the Go-around - Thanks