Weather Radar Tilt Calibration

[Mephistopheles]

Any ideas how the wx radar tilt calibration is checked to be correct(i.e. the tilt shown on the ND corresponds to the actual antenna tilt) by the avionics guys since I have often wondered when flying around on A330/340s that the tilt is so obviously out i.e. the ND is showing a tilt 3.0 down or more(over land) & no returns. As always filled out in the Tech log but engineering do a ground check &, surprise surprise it's ok but then fly the same A/C & the problem is still there.

[bfisk]

I suppose 1/2 vertical beam width tilt up should give no (ground) returns on land, pointing to flat terrain?

[Mephistopheles]

Yeah I remember way back there was a formula to calculate ground returns but, something is surely amiss when you start needing 5 down tilt to get them when flying over land? That's why I wanted to know how much faith can be put in the tilt indication on the ND.

[groundfloor]

Maintanence Manual stuff,try get hold of the appropriate info. It should also be in the Acceptance Test manual (Post Production) and the Aircraft Test Flight docs (Post Maintanence).

The specs would also be in the radars original documents/manual from the radar manufacturer.

Have a good one

[shortfuel]

If that can help, look in the AMM Chapter 34-41-00 page 505, you will find the subtask (34-41-00-720-050) for a functional test of tilt control:

Extract:

http://nsa07.casimages.com/img/2009/05/21/090521102644595354.jpg (http://www.casimages.com)



Don't forget one thing, IF you have a radar fitted with autotilt, it's normal not to have ground returns (or minimal) on your ND. Your autotilt radar uses E-GPWS to minimize ground clutter.
So make sure, you try it on MAN position before declaring its tilt faulty.
And no ground returns beyond line of sight! Typically 240Nm at FL370 (D in Nm = 1,23 sqr (H in ft) )

What selected range do you have for ground returns with tilt 3°DN?

[Mephistopheles]

shortfuel, thanks or the great info. I just wish our avionics guys would actually check it when we write it up instead of just saying that if the ND says tilt is "x" then the actual time is "x". Especially since our aeroplanes are getting a bit long in the tooth. Also they don't have the auto tilt function. Also, I typically have my ND range set to 160nm so when flying around 30000' over land there definately should be some ground returns.
Anyway cheers again.

[Checkboard]

... or you could read post #5, of this old PPRuNe thread:

http://www.pprune.org/tech-log/48016-terminal-area-weather-radar-technique.html

:ok:

[Mephistopheles]

Checkboard
...or you could read the thread properly...

[Checkboard]

I did - the information in that post allows you to work out the calibration of the radar tilt angle from raw in-flight data.

[Mephistopheles]

Any ideas how the wx radar tilt calibration is checked to be correct.... by the avionics guys

I am aware of how to check the tilt calibration for myself as mentioned in that post but I wanted to know how do the engineers check it's set correctly & if needed do any adjustments required. Shortfuel's post was exactly what I was after.

[ChristiaanJ]

shortfuel,
The procedure you show doesn't mention how it's verified that the stabilization (i.e., the pitch attitude compensation - from the IRS or whatever) works properly and is properly calibrated as well.

CJ

[shortfuel]

True!
But that was not Mephistopheles'request...:8

Mais si tu veux partir à la recherche de cette subtask...be my guest!
Pas le temps là :E

[ChristiaanJ]

shortfuel,
Merci vieux...

But... Any ideas how the wx radar tilt calibration is checked to be correctSince the tilt relative to the horizon is (tilt selector switch position) minus (pitch attitude), I'd expect a full check/calibration would involve both.

Admittedly input from an ancient... last time I had to sort a tilt control problem was on an F-104. But still interested.

CJ

[shortfuel]

Just found it...I was too curious...:bored:

It's another task called Antenna stabilization test by the ADIRU 3 (AMM 34-41-00-730-001).

[tvrao]

The tilt indicated on the ND comes from the selection made on weather radar control panel. The value of tilt indicated on ND is not taken from any tilt sensor located on the antenna assembly.The actual tilt of the antenna could differ from the control panel selection because of various attitudes of the air planes and due to various forces acting on the antenna assembly during flight.
When do calibration of the tilt on ground in maintenance according to Maintenance manual , aircraft roll and pitch are non existent and forces acting on the antenna during flight are also non existent.So when do calibration on ground it may show correct tilt as per weather radar control panel but in flight it could differ.Normally the weather radar manufacturers take these factors into account to see the difference is not very much.
For practical use for ground mapping,one may tilt the antenna in manual mode from control panel so that you can get the required return signal.

[shortfuel]

Tvrao - I kinda disagree with your post :

The TILT selector switch enables the variation of the antenna elevation angle in 1/4 deg. steps on a non-linear scale graduated in degrees, within a range of +15 deg. (UP) to -15 deg. (DOWN) in relation to a horizontal plane defined by the stabilization system.
This antenna elevation angle is displayed in cyan in the R lower corner of the ND and progresses in steps of 0.25 deg.
If the antenna position is different from the TILT selector switch position, a red ANT failure warning message replaces the TILT indication in the R lower corner of the ND.

[tvrao]

What is the source of tilt information display on ND?
Is it from a tilt sensor or is it coming from the selector switch on the control panel?
In many aircraft it is taken from control panel.
There are comparison thresholds before a failure annunciation like red ANT is displayed.If ANT fail comes ,then weather radar image will not be there.This is considered as major failure like RT unit failure and Control panel failure.
If the difference between control panel tilt command and actual tilt of antenna is only 0.1 to 0.24 you may not get red ANT fail indication.
Depending on the altitude you are flying it is possible to miss ground scan if antenna tilt is few tenths of degree away from normal value.

[shortfuel]

I couldn't find the threshold you are referring to in A320 family AMM.
As for the source of Tilt indication displayed on ND...no more details.

This antenna elevation angle is displayed in cyan in the R lower corner
That could only suggest that it is taken from a tilt sensor, without being very specific.

But even 0.24° degree error...is not a big deal :ok: