"a" wrote in message
...
On Aug 11, 3:49 pm, C Gattman wrote:
On Aug 10, 12:41 pm, john89 wrote:

I got a question regarding the so-called "elevation", i.e. the highest
point of a runway. I have been told that the elevation is usually at
the threshold, right before the touchdown zone, in order to ensure an
easier take-off.

This information is available to pilots and updated periodically in
the Airport/Facilities Directory and the US Terminal Procedures, etc.

The A/FD defines it's "elevation" figure as "the highest point of an
airport's usable runways measured in feet from mean sea level." In
addition, the A/FD lists runway slope when it is .3 or greater for
airports that have instrument approaches and elaborates based on other
runway criteria ( or than 8000', etc)

For IFR purposes, the A/FD and approach plates include a Touchdown
Zone Elevation (TDZE) for specific runways.

Pilots, particular under IFR, are expected to be familiar with runways
of intended use and, if required, alternate airports. We're strongly
encouraged to study other airports along the route in case we need to
divert. Cheers!

-Chris
CFI, KTTD

I must qualify for 'least sensitive' pilot here. I've made a number of
landings with Wx close to minimums, nasty weather, cross winds, night
time, and all that stuff. When I look up at minimums and see VASI and
runway locater lights and all that good stuff, I'm real happy to go
down the last couple of hundred feet, flare, and become earthbound
again. From the moment I go visual I really don't care what the actual
altitude of the runway I'm approaching is, I can see it, and know what
I have to do to fly the miss if needed. Does it really matter if it's
at 469 feet, or 500, at that point to those of us messing around in
SELs like Mooneys? What am I missing here?

Funny you should ask... :-)

Speaking as a former avionics technician and also student pilot, who also
rode "shotgun" on a few single pilot IFR flights back in the day, you are
exactly correct. It just happens that, in addition to the dedicated
"simmers" who stop by from time to time, this forum also serves as a source
of information for a lot of beginning students--and also for future pilots
and other interested citizens who have never been inside the airport fence.
Therefore, they are not necessary aware of which portions of the information
which is required to be surveyed, and entered into databases and onto
charts, arereally trivial in normal operations.



Even if a CAT 3 landing
(not in MY airplane!) the radar altimeter controls yoke back pressure
at flare, doesn't it? It's looking at actual wheels to ground
distances, not some indirect measure like "corrected altimeter
subtract field elevation equals air between wheels and ground.

I have no personal experience with Cat 3, so I can not address the
interconnection between the radio altimeter and the autopilot; but...

Back in the day, I was a "fill in" for the regular radio altimeter
technician--so here foes: The radio altimeter, which provides the
information regarding the flare in precision approaches, measures the
distance between the ground and the radio altimeter antenna--corrected for
the height of the antenna above the ground in the typical landing attitude.
On large transport category aircraft, that is typically several feet lower
than the antenna position when the aircraft is at rest. So, in practice,
you are exactly right about the reading of the radio altimeter in the
process of landing with the expected attitude and flap deployment.

BTW, on very large aircraft such as the Boeing 747, where the pilots eye
level at the time of touchdown is too high to give a reliable height
indication relative to the runway, it is common to also use the radio
altimeter as an information source in initiating the flare.

Peter

The other minor blimp in all of this is I set the kollsman window,
then verify the altitude indication is within specification of
published altitude. The difference in altitude between the reference
datum and my static tube could be pretty significant -- something I
had not thought about before. 20 feet eats up a lot of a 50 foot error
budget.