The reason that VDPs were developed is (as always) because of an accident. A
flight crew mistakenly identified the lights of a carnival with the runway
environment and descended early...into terrain. There is no excuse, no
loophole, for descending early....the consequences might be tragic. If you
fly the approach as if no VDP is provided, you will maintain the MDA until
you either pick up the runway visually or reach the MAP. In any case, in
murky conditions pilots should stay about 50 feet above touchdown zone
elevation until they see the green lights pass beneath the aircraft
(Gardner's Rule of Longevity).

Bob Gardner


Bob Gardner

"MH" wrote in message
...
It's my understanding that if an instrument approach includes a VDP, you
should not descend below the MDA prior to reaching this point. If you're
not equipped to identify the VDP you should fly the approach as if no VDP
is provided.

I've been told you're not _authorized_ to descend prior the VDP but that
makes little sense. If you fly the approach without being able to identify
the VDP you may well descend prior to the VDP without even realizing it
and that would still be acceptable.