Looking at some visual approach charts for SW France, I keep bumping into the abbreviation "MEHT" in connection with PAPI systems. I know it means "Minimum Eye Height over Threshold" but what's the significance, and why would that information be given on a visual approach chart? I have googled, but haven't been able to answer my question...
An A380 can also perform a visual approach and there the distance between the pilot's eyes and the wheels is very different from your average Cessna 172...
Yeeeees, and...? I know I'm being a bit thick here, but I have zero idea what the pilot does with this information, and I'd really like to understand...
If you visualise the glide slope to the runway of the PAPI, you'll see that when flying a C172 your main wheels will be about 2 meters from your eyes position which follow the gildeslope. On an A380 the main wheels can be about 50 or so meters behind your eyes position. If you follow the exact same glide with your eyes you can image that the main wheels of the A380 might touch down to early in respect to the C172. Your eyes follow the gilde slope, not the wheels.
Thank you, much appreciated!
If you visualise the glide slope to the runway of the PAPI, you'll see that when flying a C172 your main wheels will be about 2 meters from your eyes position which follow the gildeslope. On an A380 the main wheels can be about 50 or so meters behind your eyes position. If you follow the exact same glide with your eyes you can image that the main wheels of the A380 might touch down to early in respect to the C172. Your eyes follow the gilde slope, not the wheels.
I understand the PAPI's are set up for the Boeing / Airbus types, so a landing in a C172 wont be on the same glideslope profile, will be lower, and wont land in the same place (assuming an absolute perfect landing), but what can you, or do you actually do in terms physical flight compensation in either a C172 or a A380 based on the MEHT ? Like JoJo, I never really understood what the MEHT is practically for.
http://www.skybrary.aero/bookshelf/books/291.pdf
Section 8.5
The issue is that if you're flying something for which the eyes-to-wheels height is greater than the MEHT, you may see an onslope indication on the PAPIs and still touch down before the threshold.
Thanks bookworm. I think I have seen that doc before some years ago, but it will be good to have another read of it.
