Much better to go into the hedge at the end of the runway at 20kts then into the hedge at the beginning of the runway at 60kts...

A steeper descent angle does not require a greater acceleration to flare. The guy is talking about a steeper descent resulting from lower airspeed to begin with and I'm quite sure about this because it's in all the textbooks - centripetal acceleration = v²/r. Therefore, load factor in the flare is closely approximated with the formula 1 + v²/rg. The load factor reduces as a function of v². Or, for the same load factor you can flare lower with a tighter arc.

Note, I am not saying the margin has not been reduced. What I am saying is your explanation is wrong. It does not follow that the steeper descent angle requires “greater upward G”. That is not the problem. The problem is you have less kinetic energy available for the flare, which becomes a limit in the power off case. As the angles are quite small, the energy you are going to use up can be approximated with D x r x approach gradient, where D is the average drag. So increasing the gradient obviously eats into the energy margin. Your load factor results in a shorter radius (and this wins out over the extra induced drag) so you can save some energy (within the limit of CLmax) by increasing load factor. So in one sense, the steeper angle may lead you to increase load factor – assuming you have a margin to begin with - but that is to shorten the radius to save energy. Nonetheless, in the scenario given, of reduced airspeed, the steeper descent angle does not “require greater acceleration upward”. This stands to reason when you simply consider the fact that you have a lower vertical velocity to start with.

FWIW I think 172 driver's suggestion of reducing the airspeed below best glide is a subtle and efficient way of controlling the glide ratio in the engine out scenario. It's one option to get back to the nominal glide path. I would not be messing about with it on short final, nobody is saying is saying you should persist with some low airspeed like 1.1 Vso right into the flare.

Newtonian mechanics teaches from v = a * t , that for a flare performed in a fixed time, the additional acceleration (above standard 1g) is proportional to the vertical speed to be arrested, which in turn is almost exactly proportional to glide angle (because x = sin(x) for small x).

Similarly, if the flare is performed from the same height, then a = v * v / (2 * S) shows that the acceleration goes up as the square of the descent speed - or descent angle, for small angles.

This supports Pilot DAR’s statement that a greater acceleration is required from a steeper glide angle.

Thanks for the math, it exceeds my math skills. An element for consideration is "...flare performed in a fixed time...". If you're descending at a slower airspeed than recommended for the the airplane, It will slow more quickly as the nose is raised to flare - so the time available to flare will be less. If the pilot is highly skilled, it may work, but it otherwise eats into the margins which most pilots need to do a nice landing. It can be the unexpected slowing in a slightly misjudged flare, which leads the pilot to add a last moment burst of power - if it's available....

The key takeaway is that by gliding at a slower than recommended speed, you are reducing your room for error on several sides at the flare. To achieve an acceptable landing, you'll have to judge your flare altitude with greater precision, as once you begin the flare, you won't have reserve energy to pause it to correct for being too high. And this leads to having to perform the flare all the way through to touchdown as one well judged transition.

The increase in G at flare for a slower than recommended speed is as I said, slight. But, that slight increase one of several elements which result in a reduced margin for error. When you combine reduced margins, the effect is multiplied. On the face of it, if you choose to approach the surface power off with less energy (speed) than recommended, the need for pilot skill increases exponentially. Once you try this non recommended technique at altitude, you'll realize that it's a skill not worth building, when simply flying good power idle approach and landings as recommended is a more appropriate skill to build.

I found that training for slips it is good to have the students go right to the practical slip limit, in order to impart confidence in the maneuver...Of course, it not only works for landing, but side slip can also be used to do an emergency decent for fire or smoke.

Not only can be used, is recommended!

Gentle reminder from my recollection of Cessna high wing series 150 /172 is that slips with flaps extended were not approved, or perhaps this has changed ?

Quite a while ago I crunched some numbers using very generous speeds and sink rates for demonstrating the impossible turn and the calculations showed numerically that I would still crash
I was trying to find it here on pprune but so far can't...

C150/152 have no restriction regarding slips.

Some earlier 172's have an "avoid slips with flap extended" placard, but it's not unapproved. The 172N is an example. Though it also has an amplified procedure under "Crosswind Landing" which says:

The wing low method would be the beginning of a slidslip.

Other 172 models have notes which vary in this regard, but none prohibit slips with flaps extended, or the plane would not be certifiable. For the 172S, it's a recommended procedure for a wing fire in Emergency Procedures.

All Cessnas can be slipped with the flaps retracted, which is a good starting point if you want down, flaps can be extended later.

Cessna 172H POH - Slips are prohibited in full flap approaches because of a downward pitch encountered under certain combinations of airspeed and sideslip angle.

My guess is this prohibit clause with 40° flap may have been why later models no longer had 40° selectable.

Yes, Megan, for the 172H, you're right. Though, the note about crosswind landing technique is pretty similar to the one I quoted from the later model 172, so a little inconsistant. That said, the POH for the 172H was written prior to the "GAMA" format (around 1977), where the terminology of "approved", "avoid" and "prohibited" were standardized.

The 172H was certified to the following:

The present FAA requirement for this reads:

I think that this often quoted and discussed "limitation" for certain 172's comes as a result of varying interpretations and phraseology over the decades.

Ultimately, if the model of airplane you're flying says something's "prohibited" it is. Otherwise, "Avoid" is a caution, not a prohibition.

Lol...yes indeed

I can guarantee you that's not how I would explain it:E

I'm sorry, but I have to flag-up yet another quote from the brilliant radio 4 series, Cabin Pressure. When Arthur asks how an aircraft stays in the air, Martin tries that explanation:


MARTIN: .... Listen carefully, Arthur. The wing is curved on top but flat on the bottom. When it meets the air, it's split in two. The air that goes over the top has further to go, so it has to go faster to keep up with the air underneath, that reduces pressures above the wing, giving us a lift.
ARTHUR: Ah, fantastic! Thanks, Skipper. I, I totally get it now.
MARTIN: You are welcome.
ARTHUR: Except, why does it have to?
MARTIN: Why does it what what?
ARTHUR: Why does the air on the top have to keep up the air at the bottom? Why don't they just..split up?
DOUGLAS: For the sake of the kids?

Speaking of Old Bridge Airport, here's another incident - well, accident actually - from three days ago...

Same machine as the previous video :-(

Interesting software in use to have the camera auto-track the incoming aircraft...

Good on ya mate. You know what you’re doing.

I try, Rozy1, I really try...thank you

I don’t normally pay too much attention(as in try to analyze) student accidents as I just put it down to someone who basically doesn’t know how to fly an airplane.

Once the pilot has met a standard, such as a private licence, I seem to take more interest.

I know……bad attitude on my part and I shouldn’t think that way as there is always something to learn. And not all pilots need a license.

Anyways, I suspect this is a case of the student freezing at the controls with a gross over-reaction of full aft control column input trying to ‘get out of there’.

There was a case of an older graduate from my school when the trajectory looked identical. Terribly with 3 casualties, the pilot's chair slid back resulting in a pull on the yoke and his inability to recover the excess pitch.