Weather Radar Tilt

[Rubberjungle2]

Hi guys!
Could someone please clarify something for me?
Using your weather radar units in heavy jets, what is the purpose of the tilt function exactly?
I know it effectively moves the radar dish up and down so you can see tops/bottoms of CB's, but is it referenced to the aircraft attitude, or the local horizon?
ie: if you have tilt set to +6 degrees and you are climbing with a pitch attitude of 6 degrees, is the radar pointing at +6 degrees from the horizon or +12 from the horizon?
Thanks

[PRNAV1]

Average beam width is 3 degrees. 1.5 up and 1.5 down.
It's on aircraft attitude. So if you set zero it still reads 1.5degrees up if your aircraft pitch is zero.

Hope this helps...

[zerozero]

Hi Rubberjungle

This is from my manual:

<<The tilt control adjusts the beam direction plus or minus 15 degrees from the horizontal axis of the flight path. The primary area of radar detectable water is between 18,000 and 32,000 feet. During the initial climb, tilt up is required to survey this area. High altitude operations require tilt down.

Stablization circuits maintain the beam level with the earth to keep the same sweep during banking. The same stabilization maintains the tilt selection, keeping the same angular displacement of the beam during pitch changes.>>

Also:

<<Tilt-The following approximates the correct setting during takeoff and climb:

Takeoff: +4 deg
Mountainous terrain: +5 deg
10,000MSL: +3 deg
15,000MSL: +2 deg
FL200: +1 deg
FL250: 0 deg
FL300: -1 deg
FL350: -2 deg>>

Hope that helps.

[Centaurus]

And don't forget to select maximum gain control (not calibrated or auto gain)
when cruising at high altitude in order to stand a chance of picking up a cb top that will not show up in auto gain.

[JG1]

A good way to set the beam level (ie. approx parallel with the ground) is as follows, and works for any altitude :

1. Tilt the beam downward until you get ground return at the distance in miles of your height in thousands of feet.

eg. if You are at FL330 and the elevation is 3000', your height is 30 (thousand). Tilt the beam downwards until you get the edge of the ground return at 30 miles.

2. Tilt the beam up 9 degrees. It will now be very close to level.


Safe flying!

[Empty Cruise]

JG1,

I think that setting the beam to zero deg. elevation is not an aim in itself. What matters is picking up returns, and only way you do that at FL330 is scanning down.

If you scan down untill recieving ground clutter returns at your selected range, you're sure to have the beam covering everything between you and the ground - provided you select a suitably short range, i.e. no more than 160NM. If you work at this range, remember to zoom in to, say, 40 NM at intervals to make sure nothing is building below & in front of you. Or - do as all the lazy ones do and stay at 80 NM range for PM - that leaves PF free to select any range he/she might desire.

Cheers
Empty

[Trim Runaway]

When it's showing ground return it is also easier to spot radar shadows and since top of clouds won't give strong returns your more interested in what is below the top. Tilting down (untill ground return is showing) is therefore in my opinion a good way of using the wx radar.

[Alex Whittingham]

The beam is usually (always?) stabilised in pitch and roll, within limits, to the earth horizontal operating on an independant gyro-stabilised platform in older aircraft and taking feeds from INS/VG or IRS in more modern aircraft. Thus 1º pitch up should have the centre of the beam one degree above the earth horizontal irrespective of pitch attitude and the beam continues to scan level from left to right in a normal turn.

Scanner tilt operates from 15º up to 15º down.

You can calculate the relative height of returns using the formula:

[(scanner tilt - half beamwidth) ÷ 60] x range in feet

or, if you assume there are 6000ft in a nautical mile:

(scanner tilt - half beamwidth) x 100 x range in NM

[Rubberjungle2]

Ahhh....
Thanks for the replies.

It seems we have a difference of opinion!

I must admit, my understanding was with Alex W, in that it is IRS stabilised to earth horizon, not aircraft pitch attitude; ie: 5 degrees up on the wx radar will display 5 degrees up from earth horizon irrespective of aircraft pitch attitude.

Unfortunately, I'm unable to find the definitive text in any honeywell reference book.

Cheers!

[Intruder]

There is no definitive answer because it depends on the installation.

The 744 is referenced to the horizon, not the aircraft. Not sure about the 742 (which has more than 1 variety of radar).

[Helipolarbear]

Tilt function is also a helpful bi-product of the WX Radar with a Helicopter C of G displacement due to load profile and fuel burn!!

[Vimd23]

As per the B737 FCTM

It says somewhere in the Flight Crew Training Manual , that u can use the Flight Path vector ( FPV or Bird ) as a reference to set the tilt . Have found it works quit well that way.

cheers
vimd23

[Dream Land]

Tilting down (until ground return is showing) is therefore in my opinion a good way of using the wx radar.

Yes, as long as they can depict the display, hilarius deviating around planet earth.

[Jambo Buana]

This is a good method for finding the bottom of the beam.

Tilt down until you paint ground halfway down your range. Note the tilt angle. Lets say - 2 degrees.

Then take;

Your current Flight level / Wxr range (ie 330/160) = +2.1

-2 + 2.1 = +.1

So set the tilt to 0 degrees which now has the bottom of the beam at your level. Any targets showing will be at or above your level. Personally I would set about 1 degree below this value to ensure you are not over scanning a target.

Tilt management is a dying skill! You gotta practice to make perfect in this discipline.

[rhovsquared]

Definitely gonna print this page out, what Excellent suggestions !!!

N.B i will still read the AFM for specific guidance if possible, but alot of times there not much and WXR would actually be an extreme luxury for me

g'day

rhovsquared

[captain_jeeves]

Originally Posted by Centaurus

And don't forget to select maximum gain control (not calibrated or auto gain)
when cruising at high altitude in order to stand a chance of picking up a cb top that will not show up in auto gain.

Would you be kind enough to post your source of information for this procedure? Which radar manufacturer, aircraft FCOM, requires that this technique is used?

Cheers

[captain_jeeves]

Originally Posted by Dream Land

Yes, as long as they can depict the display, hilarius deviating around planet earth.

Displaying ground returns on the outer edge of the Display is one of the most effective methods of using weather radar, as it servers a number of purposes. Furthermore, it is a recommendation from several manufactures.

First, the ground return constantly tells you that the system is working.

Second, since we know the diameter of the beam for our specific aircraft - based on the diameter of the antenna - we know how much tilt is actually required to obtain a ground return, therefore, we know approximatly where the ground returns should begin. Furthermore, any return occuring between the ground return and us, can be easily and continually interpreted

Third, if we can see a ground return behind potentionally hazardous weather, then we know that there is no attenuation occuring. However, if you see a shadow, and can not see a ground return behind it somewhere, you now have a better understanding of the seriousness of that weather return.


Most important. If we are in an area where hazardous weather could occur, and we are displaying a ground return on the outer edge of the radar display (160 NM range as the radar is not very useful beyond that distance), we are gauranteed to be scanning through the freezing level at some point. Would anyone dispute the usefulness of knowing the water content at that level?


By the way. Most Transport Catagory Aircraft have a 30 inch radar antenna. There is an inverse relationship between the diameter of the antenna and the diameter of the beam. Those of use who flew smaller aircraft before moving to jets, recall how useless the radar seemed to be.

Why? A 10 inch antenna produced, an approximate, 20 degree radar beam. Not to useful.

However, the 30 inch produces a 3 degree beam; much more accurate. And, the center of that beam is on the horizon when tilt is set to "Zero" (IRS function). Therefore, the bottom of the beam is 1.5 degrees below the horizon at all times, but will only display until the radars emitted energy eventually runs out.

[TomConard]

RADAR tilt

Captain Jeeves' brief description of how to use the RADAR is EXACTLY how the Airbus SOP describes. Further, and it's been a long time ago...so my memory is a bit faded, that's how Bendix and Collins explain it, too.

My advice to those working for an airline: FOLLOW YOUR AIRLINE'S SOP!!!!

To those who use RADAR in a non-airline structure, READ THE INSTRUCTION MANUAL!!!!

Whatever you do, please do not learn how to use an airborne weather RADAR system by listening to your mates' 'techniques' as discussed in the local pub. At some point, sooner or later, the rattlesnake will bite your arse!

Tom

[BOAC]

You may wish to refer to this thread which also mentions the excellent radar training from Archie Trammel - just a Googleclick away!

From experience I fully support Centaurus on 'Max Gain' - in a 737 anyway. If nothing else it gives you plenty of time to take a "10 right for wx" instead of "hey - where did that come from? Request 40 right"

[captain_jeeves]

Originally Posted by TomConard

Captain Jeeves' brief description of how to use the RADAR is EXACTLY how the Airbus SOP describes. Further, and it's been a long time ago...so my memory is a bit faded, that's how Bendix and Collins explain it, too.

My advice to those working for an airline: FOLLOW YOUR AIRLINE'S SOP!!!!

To those who use RADAR in a non-airline structure, READ THE INSTRUCTION MANUAL!!!!

Whatever you do, please do not learn how to use an airborne weather RADAR system by listening to your mates' 'techniques' as discussed in the local pub. At some point, sooner or later, the rattlesnake will bite your arse!

Tom

If there was ever an ABSOLUTELY correct answer to this question, and to MOST other aircraft operating questions, TomConard has just provided it.


For the nay-Sayers, let me share this:


By following the airlines SOP, and the aircraft manufacturers recommendations - in 25 years of professional flying - I have never encountered a time when those recommendations jeopardized the safety of flight. Anyone who has should seriously consider whether they fully understood those SOP’s and recommendations.


Regarding Weather Radar, by using the recommended procedures (Assuming that MAX GAIN is a manufacturers recommendation in the 737 – I don’t know, but it’s not in the Airbus), I have never found myself in Weather conditions that were not expected, or easily manageable.


So, what has this experience taught me?

Do as the Manufacturer recommends – when using the equipment that THEY designed and build – and a safe flight will prevail.