New Instructor page: "Touchdown"

[cavaricooper]

Torrence-

An unabashed fan.... Glad someone picked up on it!

Best- C

[Will]

One more thing, of low importance...

On the Touchdown page, the item Deviation from VREF (aim for ±6 kts) might need both a minus sign and a plus sign on the result, instead of no sign when positive and a minus sign when negative. The lack of a plus sign makes it a bit ambiguous, especially because of the preceding ±6 remark, meaning that a positive result, without a sign, could be interpreted as a ± value, as opposed to a positive value. Once people get the hang of it, they'll understand, of course, but putting a plus in there would be a tad more clear.

[Hardy Heinlin]

Touchdown distance and pitch have no plus either.


|-|

[emerydc8]

I second the idea of displaying the "automatic flight" status.

A fix for that is to do it with a 30-knot crosswind. Then you will know if it is hand-flown or not. On the left is my manual landing. On the right is the autoland. Both using flaps 25. Of course, 25 knots is the limit for the autoland, so it's good practice to hand-fly this one. This was my best of five. Here's the situ. It starts in motion so you have to disconnect once stabilized.
https://drive.google.com/file/d/0B-WRh0Hf7VdZeHpWZFYwZWpSY1k/view?usp=sharing

                               MANUAL                                                                         Autoland

[Kieber]

Just a few words and my thoughts about "deviation from Vref (aim for < -/+ 6 kt).
I think this "aim for < -/+ 6 kt" looks like you were still safe when flying till 6 kts below Vref, but it isn't.

As far as I can remember, we always used the wording "+..., - 0(!) from the recommended approach speed". In the meantime I forgot the +value. A speed drop below Vref was an absolute no go, like a car jumps a red traffic light or a train jumps a red signal! (The professional jargon on check rides was "killing item").

Our absolute minimum recommended approach speed was Vref +5.
In wind conditions of more than 10 kts we added a wind correction. The recommended wind correction was 1/2 the steady headwind component (1/2 the steady wind if not runway limited) plus all of the gust value, based on tower reported winds. The maximum wind correction should not exceed 20 kts. In all cases, the gust correction should be maintained to the touchdown while the steady wind correction should be bled off as the airplane approaches touchdown.

Consequently to the above, the speed bug was set to the above described recommended approach speed. (Vref +5 or Vref +wind correction to a maximum of Vref +20).

So I think, we have to find another term for Vref in "deviation from Vref" and change the 6 into a 5 in (aim for <-/+6 kt)".

My suggestion: "deviation from Vref + correction*  (aim for <+/-5 kt)". In this case it is assured you should never drop below the Vref speed (although we never accepted a drop below the recommended approach speed and used "aim for + ..../ - 0 kts"! See above).
*The term "Vref + correction" maybe changed to Vref + wind correction, approach speed, bug speed, target speed, Vref additives or so.

Maybe somebody like Peter (Britjet), Hardy or another forum member here has a better idea.

Regards
Walter     

[Hardy Heinlin]

Thanks, Walter.

I understand that a negative deviation is a no-go, but this data is recorded on touchdown. So I guess the Vref deviation on touchdown is rather irrelevant for touchdown analysis? Maybe it's better to record the offset from the stall speed instead?

Or I keep the Vref deviation but record it when passing 50* ft AGL instead on touchdown?


Cheers,

|-|ardy


* Or at 25 ft AGL, i.e. at the point in time where airspeed control ends.

[Kieber]

Whoops.......it is a fundamental misunderstanding as far as I am concerned......

I figured the Vref deviation is for the approach part. So, I think, it is OK.

Sorry
Walter

[Hardy Heinlin]

Well, it's me who is responsible for that misunderstanding :-)

I think it's better to record the Vref deviation when passing 25 ft AGL, i.e. at the point where you start retarding the throttles and where the target changes from airspeed control to pitch control.


Cheers,

|-|ardy


P.S.: And instead of "VREF" the text shoud better read "MCP SPD" and the record should take the MCP SPD as a reference. This way it would include any wind additives automatically.

[Hardy Heinlin]

New text:

[tango4]

Just a quick remark:

I really like this idea of checking speed at 25ft. I agree it makes more sense than VRef at touchdown.

I think I would just somehow explain that the reference is MCP Speed and not VRef. Having followed this discussion and being familiar with Boeing approach speed philosophy, it does make sense, but it might not be obivous for everyone. Something like:

"Speed deviation (from MCP SPD) at 25ft (aim for 0 to +5kt)"

I think otherwise, you can expect some questions, but I might be wrong.

Anyway, thanks a lot for this page, really a very nice idea.

Charles

[Hardy Heinlin]

At first I wrote "speed bug deviation". But that was too long.

It's not MCP SPD, it could also be FMC speed when the MCP window is blank. It's simply the speed bug on the PFD.

I think the meaning of "speed deviation" is obvious. If not promptly, then after the first try.


|-|ardy


Now available in 10.0.9g:

http://aerowinx.com/board/index.php?topic=3685.0

[Kieber]

It's simply the speed bug on the PFD.

I think the meaning of "speed deviation" is obvious.

|-|ardy

I really like this idea of checking speed at 25ft. I agree it makes more sense than VRef at touchdown.

Charles

I agree gentlemen. Things are shaping up well....

Walter

[acannata]

Hi!

I'm so sorry to be again a dissenting voice
In my opinion it is fuzzy to know the early flare (but it depends also on the timing of the flare that may be different among simmers!) airspeed in a touchdown analysis.
Airspeed at touchdown is much more interesting, because of its relationship to body attitude and the risk of body contact. In my copy of B744 FCTM (oct 2008), there is a graph showing such relationship. Moreover, in the document Boeing says: "...airplane body attitudes are based upon typical landing weights, flaps 30, VREF + 5 (approach) and VREF + 0 (landing)"; and later in the text: the graph "shows normal airplane attitude at touchdown speed for flap 30 (VREF 30 to VREF 30 - 5 knots).
I recognize that in case of a consistent wind correction to Vref it is difficult to say which value should be recorded in the touchdown analysis.
Anyway, I appreciate very much to know TD distance from threshold and deviation from centerline. Really a Precision Simulator!
Cheers

Aldo

[Hardy Heinlin]

But below 25 ft AGL you won't focus on speed anymore but on pitch. The quality of your flare and touchdown depends on your speed at 25 ft. If you get that right and if you get the pitch control right thereafter, your VREF deviation on touchdown will automatically be right as well.

This is an analysis of the pilot's flying skills, not of the structural status of the aircraft. If you want to know what you're doing wrong as a pilot you need to know something about the aircraft movement and not about the point where the movement ends. At the end you can't change the end anymore. That's also the reason why there is sinkrate data to get an idea of the movement rather than g-force data which is something the pilot can't see and control during the maneuver.


Cheers,

|-|ardy

[acannata]

Hardy,

a reply not to question your choices for PSX, but only discuss the issue
I agree that a good landing depends on a good approach. Nevertheless..
Look at this scenario. My airspeed at 25' AGL is correct, but I want be a greaser. So I make a very long flare pitching up the aircraft. Airspeed bleeds off too much before touchdown. So the aircraft falls from the sky and I experience an hard landing. In that scenario 25' AGL airspeed seems to be ok, but it does not explain the poor performance on landing. In other words, airspeed at 25' is representative of final approach flying-skill, but it does not correlate necessarly to flying skills during flare and touchdown.

Aldo

[Hardy Heinlin]

I disagree. If you flare too far you will notice your distance from the threshold is far beyond 1500 ft, and your pitch will be too high if the airspeed decreases, or your pitch will be good but your main gear touchdown will be too hard due to the decreasing lift.

You see: All parameters depend on each other. If any of them is not perfect, the whole landing is not perfect.


|-|ardy

[Britjet]

I suggest you watch my video "landing". In there (somewhere) I actually talk the "30, 20, 10" rate as it should sound.
This assumes a rate of descent that is held constant all the way down to thirty feet. We used to teach that the flare starts at the T in thirTy. Any raising of the nose before that that will result is an extended landing distance, and anything after that is likely to result in a hard landing.

I have done a few landings recently in PSX and it is my opinion so far based on my own efforts that you should be getting a touchdown rate in the region of 300 to 400 fpm. I think 200 is a "floater". (Sorry Hardy).

I will post some more info on this after I get chance to experiment further.

Flare pitch should not go higher than 5 degrees ideally. With a little as 7.5 even with wings level you can get a tail-scrape. So much so that it requires a callout of "Attitude" or similar in some airlines.
If you want to do it properly don't try for "greasers" ;-)

Peter

[Hardy Heinlin]

According to engineering documents, autoland aims for 90 fpm at touchdown.

I know that autoland floats a tiny bit further than a typical manual landing, but it should be obvious that the targets of a certified autoland system lie well within the allowed tolerances; in other words: 90 fpm can't be wrong. On the other hand, on a manual landing, you typically get about 300 fpm. The "200" in the text is an approximate average. It shouldn't be considered too academically; give +/- 100 fpm here, just like +/- 1000 ft to the threshold distance etc.

Of course, as you have 25 feet to go, the final sinkrate at 0 feet depends on how the flare curve is shaped: If the curve looks like an arc, you will float very far; if it looks like an exponential "J"-hook, you won't flare far, but you still get a soft touch at the end.


|-|ardy

[Britjet]

Well, a real autoland is notably different from a manual landing. The aircraft makes quite an abrupt pitch up at 50r and then flies quite a flat attitude to landing - hence, I think, the increased quoted landing distance..
Peter.

[emerydc8]

Well, a real autoland is notably different from a manual landing. The aircraft makes quite an abrupt pitch up at 50r and then flies quite a flat attitude to landing - hence, I think, the increased quoted landing distance..
Peter.

I agree. Not to open a can of worms, but I am pretty sure the autoland touchdown point is actually about 2500' from the threshold.