London City

[Hobbit]

Two questions for all you technically minded folk with reference to LCY.
1. Where does it say that a grooved runway can be treated as dry? When do have to start using wet performance information?
2. By violateing the 5.5 degree glideslope do you extend your landing run and invalidate your landing performance?
Any answers would be much appreciated.
Thanks

[OverRun]

On the issue of grooved and dry,some of this has been cover3ed in earlier PPRUNE's - try
http://www.geocities.com/profemery/aviation/runway_damp_dry_wet_grooved.html

[CJ Driver]

By "violate" I assume you mean ducking under the glideslope on short final to make the view out the front seem more normal - which is of course very tempting.

Your operating procedures may be different, but our SVref (steep Vref) is faster than normal Vref. When we arrive over the threshold at LCY we flare lower, but more aggressively, than on a normal arrival. In our aircraft this "firm pull" bleeds off a lot of energy quickly - I can also confirm from experience that if it's mis-timed even slightly, the stick shaker will clatter as we touch down.:ooh: The general result is a firm arrival with a nice short landing roll.

My understanding is that if you duck under the glideslope to achieve a normal profile in the last portion of descent, the flare and touchdown will be more "normal", but you'd better flick over to the normal landing distance tables, rather than the steep approach ones.

Glancing at our Ops manual, I can tell you that at a typical heavy-ish landing weight, the factored landing distance for a 5.5 degree "firm" arrival, on SVref, sea level, ISA, no wind, would be 3740 feet. Same conditions, for a normal 3 degree "smooth" arrival, on Vref, factored distance would be 4350. Bearing in mind that SVref is actually 5 knots faster than the corresponding Vref, the duck-and-smooth-it-out strategy could actually take somewhat more distance than that.

So the short answer is - yes, ducking under will extend the landing run and invalidate the landing performance data.

[Crossunder]

It all really depends on how you execute the flare. A helicopter will have the shortest ldg distance, using a 90deg approach angle. The flatter your approach angle, the longer the ldg distance. But; you also have to consider the flare itself. A flatter app angle might enable you to go below PAPI and just "fly it onto the runway", thus achieving an early touchdown point. With spoilers, max braking and thrust reverse activated earlier, your ldg distance will decrease. However, the AOM does not have any graphs or tables for this, so you'd really be on your own ("they called it pilot error") if something happens...
I guess what I'm really trying to say is that it's the touchdown point and touchdown speed that determine your actual landing distance, and that this depends on technique. I fly the Dash-8, and with a 800m runway, 4.5 - 6deg PLASI and slippery runway, I can understand those who go below the PLASI and move their aimpoint closer to the beginning of the runway. It's too easy to mess up the flare and suddenly have a lot of unusable runway behind you.

[FlyingForFun]

A related question, in that case: why, when I was taught to do a short-field approach in a piston-engined aircraft, was I told to come in flatter than usual?

FFF
--------------

[Crossunder]

You'd better ask you IP about that. Could be that he/she was wrong... ;-) Don't swallow hook, line and sinker without stopping to think for yourself, not even my posts :-)
...or maybe "flatter" meant "lower than usual", thus giving a different touchdown point (inside the RAG of course...)?