LHR 09 Left approach
 

Just how high are aircraft landing on 09L when they pass over the spotting location on the A3044? Looks like no more than 100 feet to me.

From Google Earth it would seem that the road is 700 metres from the landing threshold.

Aircraft usually cross the threshold at about 50 feet.

By maths that would suggest that they cross the road at about 170 feet.

If you use Google earth to measure the distance from the spotting location to the 09L TDZ it gives 3800 feet. Assuming a 3 degree glideslope a bit of trigonometry gives 190 feet above the ground as they pass over the spotting location. (and assuming that the spotting site is the same elevation as the TDZ)

Obviously some aircraft land a little longer and some, fewer, a little shorter but 744,77E or 380 look pretty darn big at that height

Thanks. I thought of doing that calculation but I didn't know where they touched down relative to the marked threshold.

I took the touch down point as the area on the runway where the solid block white markers morph into a sort of pair of blocks joined by another block on either the left or right depending on side of the runway. I think the Papi indicators are located next to them as well and that probably further down the runway than TB suggests and quite along way down from the zebra crossing threshold marks. But with his answer of 170ft and mine of 190 its a pretty good indication of how high they are over the spotting point. Talking of which is that an actual layby or set back from the road or does it involve an illegal yellow line parking job
PB

My measurement was to the runway side of the road. If the spectator area is on the west side, it would account for some of the difference.

As PB says, we are pretty much in agreement.

Strictly speaking, the Touchdown Zone (TDZ), per the ICAO definition, is the first 2500 feet or so of the runway after the piano keys, delineated by the solid white stripes either side of the centreline.

The markings part of the way along the TDZ adjacent to the PAPIs indicate, in ICAO-speak, the aiming point. The relationship between the aiming point and where a given aircraft will actually touch down depends largely on the aircraft geometry.

My point about the height crossing the threshold (it seems to be 51 ft at LHR 09L, rather than the 50 ft I said, but what is a foot between firends) is that is what determines the height further back up the flight path, assuming the aircraft is on the glideslope. Where it touches down is not strictly speaking relevant.

For the B747-400 (my last type), the glideslope antenna used on the final part of the approach is on the main landing gear door, iirc (earlier on the approach it uses an antenna in the radome, again iirc).

HTH

DR and TB Thnaks you for polite, informative and interesting points you make -and my apologies for the wrong terminology I wasn't sure what the aiming point mark should be called and of course I was wrong in referring to it as the TDZ (the bit with ll the pretty lights at night ).

As pointed out aircraft like a 747 are so big that different parts of it are significantly higher/lower than others - the difference between the pilots eye level and the trailing gear bogie is pretty big on a 747 as is the chosen potion of various sensors. Either way i think we all gave the OP a pretty good answer to his question .

I havent stood under the LHR approach for a few years but when it comes to impressive size of aircraft the pub car under the approach at Farnborough was an interesting place to be when the first A380 landed there. Literally blocking out the sky, but as to how high it was, well the aiming point on Rwy 24 is almost halfway down the actual paved surface as opposed to the marked out runway and i know it was empty but still impressive stopping in the distance available. As another point of interest the Google earth picture of Fnb pretty clearly shows up rubber marks fairly equally distributed either side of the aiming point on that runway something that didnt show up on LHR 09R

The bird's eye views of LHR on Bing Maps (particularly the one looking east) show the amount of rubber deposited on the TDZs. It's particularly noticeable if you compare 09L and 09R - the former is much darker, reflecting the fact that there are relatively few landings on 09R as there is no runway rotation on easterlies.

09L
 

Of course we await the Planning Inspectors decision soon on the use of 09L for departures mixed with 09R. Also HAL have recently provided information that a displaced threshold is in use on 09L 0.55nm when using the 3.2 degree ILS, ahead of the normal TDZ so heights may vary :\

Reminds me of the time the Windsor noise freaks assured me that aircraft flew down Windsor High Street below 500 ft!

I think you may be misinterpreting the parameters of the recent "steeper approach" trial (which ended a couple of weeks ago).

Firstly, there was no 3.2° ILS at LHR - the trial involved 3.2° RNAV approaches interleaved with conventional 3° ILS/MLS approaches.

There was also no mention of changes to the existing 09L/09R displaced thresholds (each 307m) in any of the trial documentation. One possible source of confusion is that the FAF for the 3.2° approach was 0.5nm closer to the current displaced threshold than the 3° FAF.

But, HD, what would you know about it all - compared to a "noise freak" ?

that aircraft flew down Windsor High Street below 500 ft!:ooh:
The High street is roughly aligned North/South

Shows how much they knew!

I was at Hounslow Urban farm last year and I definitely saw at least 1 simultaneous 09L/09R departure, I don't remember ever seeing that before. Was that a trial?

There were just under 400 departures from 09L last year, almost all of them at night during single-runway operations.

Are you sure you didn't see a departure at the same time as go-around on the landing runway ?

Could have been I guess

Ah the wonders of Pprune -one person poses a question and we get all sorts of interesting spin offs, I am not grumbling I think it is very interesting to see how discussions develop.

I have often wondered how long the Cranford Agreement would last re 09L departures once LHR got extra busy, when I was a kid in my spotting days in sunny Stanwell it used to annoy me that it was always 10L /28L for landing as you only got a really good view when the airport was on Easterlies and take offs were from 10R, mind you we still had the occasional days of using the 23s as consolation.

What we have established for the OP is that aircraft are at all kinds of heights within a fairly narrow band but are pretty much never at 100 ft over the spotting spot.