Approach Timing

(Michael) wrote

This method is used by the flight control software of the Airbus A-320
series of aircraft. I **** you not. Straight from the lips of an
A-320 captain. The autothrottles adjust to a given groundspeed on
approach. Groundspeed, not airspeed. No, I don't know why either -
but he insists that it's true.

Well...I have a pretty good idea why without ever having been
in an Airbus. MicroBurst. On an ILS using a "normal" autopilot
and autothrottles, when approaching a microburst, the autothrottles
(or human pilot) will retard the throttles to maintain Glideslope
and IAS and then shortly after passing the microburst, one finds
himself with reduced power and rapidly reducing airspeed. Been
there--Done that!
By flying a groundspeed that is proportional to the strength of the
microburst on the front side of the microburst, one just might survive
the backside. Without the Groundspeed input, one just adds some
arbitrarily chosen number of knots to the IAS, wanting at the same
time to keep it as low a number as possible because you had to get
rid of any excess prior to touchdown.
In really bad conditions, indicated by a larger than normal difference
between IAS and GS, I always kept the GS up.

Bob Moore
ATP B-727 B-707
PanAm (retired)

Andrew Sarangan wrote:

Most GPS databases do not contain the
lat/lon for localizer stations.

Not sure about most. Many do.

"Andrew Sarangan" wrote in message
om...

Fly the same airspeed as always, measure the groundspeed from the GPS,
and interpolate the timing table for your ground speed.


If you trust the GPS to provide accurate groundspeed why not trust it to
determine the MAP?

On Tue, 07 Sep 2004 11:50:58 GMT, john smith wrote:

For those of you using handheld GPS's when you fly IFR:

Do you use the throttle to increase/decrease power to match the ground
speed to the approach speed table so the time is correct to the MAP?

No sir. That could, or is a very dangerous practice.
You compute the time to the MAP based on the Gs while flying your
normal airspeed on approach.


Or,

Do you use the distance to the airport to determine/verify the MAP, even
though the time may not have expired?

I use it along with the RNAV computer to give time and distance for
situational awareness.

If I did everything right the time expires when I reach the MAP (or
close to it)

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

This is not scientific in any way, but judging from the maps I have made
overlaying my GPS track on geo-referenced satellite images (using
USAPhotoMaps and TerraServer), it is extremely accurate. This track data
was made using my Garmin 196, I think WAAS was active at the time (although
it was before the official rollout).

http://home.comcast.net/~jslew/Photomap2m.png

"Jeremy Lew" wrote in message ...

This is not scientific in any way, but judging from the maps I have made
overlaying my GPS track on geo-referenced satellite images (using
USAPhotoMaps and TerraServer), it is extremely accurate. This track data
was made using my Garmin 196, I think WAAS was active at the time (although
it was before the official rollout).

http://home.comcast.net/~jslew/Photomap2m.png

Looks like you're flying one of ECAC's Warriors? Pretty impressive.

Kind of reminds me of bringing my father's sailboat up the Connecticut
River in 1/4mi viz. fog. He has DGPS and radar, and at slack tide, if
you navigated straight to where the GPS said the buoy would be, you'd
probably hit it. Accuracy was close to that provided by the radar set,
and a lot easier to read. Of course the GPS can't tell you where the
other boats are...

Everyone agrees GPS, even if "just a handheld," is probably the most
accurate navigational system onboard. It's all a question of how far
you carry that. Me, I prefer to split differences wherever possible.
Anything to increase the odds of catching a really bad error before
it's too late.

Best,
-cwk.

"C Kingsbury" wrote in message
m...
"Jeremy Lew" wrote in message
...

Looks like you're flying one of ECAC's Warriors? Pretty impressive.

Colin, good eye, but you obviously need some practice distinguishing Katana
GPS tracks from Warrior GPS tracks Actually, there's tracks from several
flights there, so it's probably a mix of both types.