Question about 74 feet MEHT PAPI systems v 53 feet MEHT PAPI.
 

Question:
In some Australian Jepps aerodrome charts, the PAPI published MEHT (Mean Eye Height at Threshold) can be as high as 74 feet. Melbourne is an example.
Launceston aerodrome chart shows MEHT as 53 feet. The 74 feet MEHT is for wide body types to account for the longer wheel base.

Does that mean with a 74 feet MEHT PAPI, the physical siting (position on the ground) of the four PAPI lights are further away from the landing threshold than a PAPI with 53 feet MEHT?

As far as I'm aware, PAPI being a point source aid, the physical location of the lights is the same (ie circa 300m from the threshold) regardless of the MEHT. I presume the angle for 'on slope' would be adjusted for the MEHT required. Perhaps someone with greater knowledge could give a better answer?

My understanding Sheppey is that you are correct. If the PAPI remained the same distance from the threshold then you would have to come in on a higher angle to cross the threshold that 20ft higher. I doubt they would change the approach path angles for that 20ft difference rather than moving the PAPI further from the threshold. I'll have to compare next time I go into the 2 different types.

Yes.......assuming same angle.

You might notice the ground-car guys (or guys and gals, at a PC airport) rushing out to move the PAPI forward and backwards for the next approach ... it's impressive how quickly they can change things when aircraft are line-up on the ILS. Of course, in low-vis conditions, you probably won't see the car.

Seriously though - seeing as the PAPI at ML (as an example) is the standard 3 degrees, the difference must be due to the PAPI being located a little further down the runway - seeing as it is a longer runway, the touchdown zone (with markings and PAPI) is further from the threshold.

As it turns out, adjusting the distance of the installation from the threshold (rather than an adjustment to the approach angle, which was larger than I had considered), to achieve the required MEHT for the runway (presumably for the largest type likely to use it) is quite right. I found the following link, which includes the formula for MEHT v Distance from threshold too, for those interested. I've learnt something new.

https://www.tc.gc.ca/eng/civilaviati...2-009-1202.htm

It isn't to do with the length of the runway, it's to do with the size of the aircraft it's designed for.

For example, MEL RWY27 is relatively short, but still has a 74' PAPI.

Large aircraft (most wide bodies) generally aim at the 1500' (450m) markers to achieve the desired wheel height over the threshold (e.g. 35'). That is where a 74' PAPI is located.

A 53' PAPI is located at the 1000' (300m) markers, and is designed for smaller aircraft (up to narrow body jets e.g. B737/A320).

Dukeunlimited. Thank you very much for going to the trouble of sending the Canadian link to PAPI angles and installations. It was just what I was after.
To other contributors, thank you also for your comments.

Can anyone shed some light on the PAPI eye heights at Adelaide? It might have been a mistake when the original VASIs were installed but the opportunity to standardise the MEHT at Adelaide has been passed up many times.

No worries sheppey! As I mentioned, it was enlightening for me too.

When Orange extended it's runway to allow for the F100 over the Saab, we moved the PAPIs about 20m. "The standard wheel clearance over the threshold for the most demanding amongst the aircraft regularly using the runway"

RAAF Base Williamtown has long been the home of fighter squadrons of the RAAF and is used by civilian aircraft. The current Air Services aerodrome chart reveals runways 12/30 have a PAPI set for a three degree slope with threshold crossing height of 50 feet.

From observation the crossing height of most jet fighters operating from Williamtown seems to be about 10 feet with aiming point to touch down very close to the runway threshold markers. Assuming therefore that "the standard wheel clearance over the threshold for the most demanding amongst the aircraft regularly using the runway and fighters use the Williamtown runways a lot more than civil arrivals, how come the PAPI is not set at ten feet over the threshold rather than 50 feet?:ok:

http://naca.central.cranfield.ac.uk/...rc/rm/3602.pdf
https://www.tc.gc.ca/media/documents...AC_302-009.pdf
http://code7700.com/pdfs/icao_annex_14_vol_1.pdf