Sure but that is A380 problem, I think go around or flare from glide at 50ft will result in wheels touching ground badly with people losing teeth due to engine & airframe inertia? go around from 50ft agl in pistons do not result in wheels touching the ground
I think it’s worth trying to follow LPV at least once in lifetime, bellow DA all the way to touchdown in typical piston at 80kts Vref (even using hood with someone doing RHS), just to see how things go, how much quality the signal has, how much options and risks one has, there is always plenty of time to flare or go around, it should give enough confidence with regards to the quality of 3D SBAS guidance as well as any concerns about low visibility, wrong altimeter setting, crashing on trees or hills, getting lost…
Surely your descent rate even on LPV depends on your ground speed. An A320 travelling on a 3° glideslope at a ground speed of 150kts would hit the ground at 750fpm.
Peter wrote:
If there is IMC below the DH and all the way to near the ground, and you have set the altimeter so it over-reads, and you are not checking DME (or GPS distance if LPV)then you will hit the ground.
With an ILS GS or an LPV GS, you will hit the runway. With a baro-derived GS you will hit the ground before the runway – like nearly happened in the Airbus case.
Peter, yes, that is precisely the point Ibra was making – if you fly LPV all the way down, then you will hit the aiming marking on the runway with less than 500fpm, which is a very firm landing, but not a crash! That’s why it is ridiculous to not have an LPV on an a/c that costs many millions.
“ you are not checking DME (or GPS distance if LPV)
then you will hit the ground.”
You may be checking your distance vs altitude acc to the app plate but that will not save you on your LNAV or RNP app on A320 or GNS430.
Your checks will be just fine but you will be below or above your profile.
In typical Cat1 conditions, you see the ground before you hit it unless you are really busy inside the cockpit…
On auto-pilot at least, you tend to look outside more often, setting wrong QNH on LPV or ILS means you will see the ground bellow DA, 50ft is enough to flare or go around in SEP? if visibility is less than 50ft vertically and 500m, one should not fly Cat1 ILS or Cat1 LPV approaches let alone fly it on wrong QNH or DA
If one is busy handflying in zero/zero conditions without synthetic vision, I can see how they would hit ground with wrong DA or QNH
If
then you will hit the ground.
With an ILS GS or an LPV GS, you will hit the runway. With a baro-derived GS you will hit the ground before the runway – like nearly happened in the Airbus case.
Most of the time one gets away with not checking DME because one has a general awareness of the cloudbase (200ft or more) and visibility, so one will get visual before it is too late. This has been a learning experience for me because I have been slack at checking the DME on an ILS and I am sure many pilots do the same; one gets fixated especially near the DH.
If the airport is below zero centigrade minima should be adjusted to temperature corrected minima, which will result in a higher DA.
Yes, as well as „platform“ altitude. But, following an ILS/LPV GS/GP, one would never hit an obstacle, even in cold temps. The „beam“ is always the same geometry. It is fixed in space. The temperature correction is important to crosscheck and verify the correct DME/ALT during the approach.
Yes late Sr22 G5 as well (I flew one that had it)
I demonstrated this to a student the other day on a G6 SR20 which can do BARO-VNAV
I think only PA46 and SRxx G6 have BARO?
A BARO-VNAV with the altimeter setting too high will make you fly a perfect 3° GP with all altitudes corresponding to distance. But you´ll be below the intended GP, going to a place in front of the TDZ.
It will be hard to catch using GS/VSI or using GPS distance & QNH altitudes
DME distance & QNH altitude can help but you may have to do it in your mind (or read ILS plate not RNP L/VNAV BARO)
