PDA

View Full Version : radar tilt for takeoff


JammedStab
19th Jun 2008, 01:56
My reading material says that stabilization adjusts for the nose-up attitude and therefore no nosedown tilt is required for compensation. I assume the same is true for nose down attitudes. We set 7° nose up tilt for takeoff. Is this standard for all airliners? Do you adjust tilt downwards during the climbout?

Dream Land
19th Jun 2008, 02:03
For those not familiar operating wx radar, follow SOP, our aircraft have automatic mode, works fine.

JammedStab
19th Jun 2008, 02:23
For those that don't have automatic mode....any responses to the original question?

PantLoad
19th Jun 2008, 02:25
The tilt of the RADAR antenna has nothing to do with the pitch of the aircraft, as the IRU, in its determination of where the horizon is, tells the stabilization circuitry where 'level' is.

So, let's say the aircraft's pitch is exactly on the horizon...that is, Zero degrees...and let's say the RADAR antenna is tilted up 4 degrees (four degrees above the horizon). Now, you pitch the aircraft up four degrees above the horizon. The RADAR antenna pitch stabilization circuitry maintains four degrees above the horizon (it moves downward as the aircraft pitches up)...based on the IRU's reference of Zero pitch.


Does this answer your question?


PantLoad

PantLoad
19th Jun 2008, 02:33
You adjust the RADAR antenna tilt, based on the range you're looking at and the aircraft's altitude. This has nothing to do with the aircraft's pitch.

Some SOPs require 4 degrees up on the RADAR for takeoff...some as high as 7. As you climb to altitude, you'll be adjusting downward the RADAR tilt.

Airbus has a great publication, "Optimal Use of Weather RADAR". It explains very well the 'how' and 'why' you adjust the RADAR antenna tilt.

One of the most common errors I see is the overscanning of weather. This is the result of not pointing the RADAR tilt down sufficiently to see the returns. CBs show the greatest returns at the freezing level. CB tops may show little, if any, return...but turbulence can be severe.

As Dreamland mentioned, the auto RADARs (multiscan) today do a great job of knowing where to have the tilt.

PantLoad

411A
19th Jun 2008, 02:34
In the Lockheed TriStar, normal radar antenna tilt for takeoff is 2 degrees up, same as in cruise...normally.
PantLoad is spot on about stabilization.

ITCZ
19th Jun 2008, 08:51
An excellent (and free) Wx Radar primer published by GAPAN:
http://www.gapan.org/Papers/Weather%20Radar.pdf

Tilt management begins on page 40.
My reading material says that stabilization adjusts for the nose-up attitude and therefore no nosedown tilt is required for compensation. I assume the same is true for nose down attitudes.
Yes.

You don't mention which aircraft and which WxRDR unit you have installed, but generally -- yes.

The antenna is stabilised by the IRU (or other means in earlier units) to be stabilised with reference to the zero plane in pitch and roll.
We set 7° nose up tilt for takeoff. Is this standard for all airliners?
It is common. The 7° nose up is a reference to the centre of the beam w.r.t the plane of the earth. It is a quick way of ensuring that any beam produced by a 12" or greater dish will not give ground returns.

In the case of an 8° beam width from a 12" dish, the bottom of the beam will be 7° - (8°/2) or 3° above the horizontal plane. That is, it will not return anything lower than 320' elevation at 1nm, 3200' at 10nm, and the bottom of the beam is scanning FL320 at 100nm range.

30" dishes fitted to airliners have a typical beam width of 3.2° to 3.5°.
Setting the TILT to 7° UP prior to departure has the bottom of the beam at 7° - (3.5°/2) = 5.3° up.

5.3 x 109 feet/nm = Bottom of the beam is elevation 577' at 1nm
5770' at 10nm range
FL577 at 100nm range!
Do you adjust tilt downwards during the climbout?
Yes. I want to scan for weather, not the moon!

Parkbremse
19th Jun 2008, 09:44
thanks a lot for the link ITCZ... great stuff! :ok:

Jumbo Driver
19th Jun 2008, 09:45
I would say a minimum of 5 degrees nose-up tilt if you want to have a look before take-off, otherwise you will be looking at ground clutter as well as any weather returns.


JD
:)

ppppilot
19th Jun 2008, 09:57
Hi Jammed.
7 up seems a little bit high to me. I have flown many types of aircrafts from heavy to medium and as far as I remember a tipical setting for the TO is 3 to 4 degrees up.
The tilt is a reference to the horizon as it has been said here. It is like to say the angle of your neck and the horizon to scan for posible traffics. At the TO you will look up, at the cruise level straight and down for the descent.
Usually at FL280 must be scanning to the horizon, but I have found that setting very relative. At medium latitudes the more activity layer is from FL140 to FL210. As you goes to northern latitudes the atmosphere is compresed and as the radar antenna doesn't understand of FL but heights. Also depends on the diameter of your antenna. If I dont remember bad varies from 9 to 16 inches wide.
So the best rule is the rule of thumb. As you see the terrain echoes disappearing at the TO it is your setting. As you climb mantain the last ring (further from you) of the radar showing the terrain echoes varying the tilt setting as you climb or change the range of the scope, always to mantain the last ring with the terrain.
If that requires 7 degrees up or 17 down is strange but then you are sure you are scanning good.
Here you have the airbus document.
http://www.copac.es/direcciones/Seguridad/AIRBUS%20FLIGHT%20OPERATIONS%20BRIEFING%20NOTES/18.FOBN.%20Adverse%20weather%20operations.%20Optimun%20use%2 0of%20the%20weather%20radar.pdf
Tailwinds :ok:
Edited to say... Consult with SNS3Guppy. He is (or was) a CB adict :E

IFLY_INDIGO
20th Jun 2008, 00:01
hi there, I don't agree with automode of weather radar.. I don't find it optimal. It exaggerate the picture very much. I fly A320-232 in India and presently it is bad weather season in India. If I use airbus recommendation : gain +8 and AUTO, I see only red on ND. It is very stupid. So I use gain +12 with Manual tilt -1deg in cruise.. It gives more realistic picture. with this setting, my experience says " go green and avoid yellow". yellow at 40nm would turn green at 15nm for sure. avoid all yellows at 15nm. It works wonderful and I don't need much deviation here and there whereas all the airplanes around me keep asking for 30 miles left right.. I smile and wish they try manual tilt someday...

cheers

Capn Bloggs
21st Jun 2008, 03:49
I agree with 7° for takeoff. This removes ground returns (unless the hills are very high) but will still paint weather. As you climb, lower the tilt until when in cruise, you're looking down slightly (edge of closest ground return about 60nm in front) to pick up the lower sections of big buildups. And if you're really "looking" for weather, not just big CBs, put the gain up to full until you find it, then lower gain to help avoid it. Quite often small buildups that produce harsh bumps won't show very well in auto gain.

FlightDetent
22nd Jun 2008, 10:39
I don't find it optimal. It exaggerate the picture very much. Whilst I agree with you, due to certain technical reasons Airbus (unlike Boeing that installs the same kit to 777) concludes that AUTO mode and CAL gain may eventually hide something from you, hence the requirement for 8+ with AUTO. As a bit of relief, you will find that according to the latest version of the applicable Temporary Revision to FCOM, 8+ gain when in AUTO is now only mandatory below FL150.

FD (the un-real)

RAT 5
24th Jun 2008, 16:59
May I digress slightly. Can anyone help with radar use, B738, when below 5000'agl on arrival? I scan ahead when about 40nm out and try to get build apicture of what's down there.
However, when close to the gorund and trying to get a clear picture there is too much ground clutter. Pointing it up us useless. reducing the gain from auto to manual is the only thing left, but how much? Might you erase the very stuff you are trying to detect and giving yourself a false relaxation. Any hills around and the screen gives you the idea than a diversion (false TS's) when you suspect there are some reals ones as well, might be best option.

I've had the confusion below 3000' that ATC radar gavde a base turn heading, but our screen looked like tomatoes. ATC said their screen was clear, and sure enough we were underneath the real stuff.

Any solid advice mch appreciated. The FCOM are useless on such an important topic. Our grey boxes don't even have the manufacturer's name/model on them to pursue that route.

Capt Fathom
24th Jun 2008, 17:17
normal radar antenna tilt for takeoff is 2 degrees up, same as in cruise...normally

2 deg UP in cruise? A man that enjoys living on the edge!

ChristiaanJ
24th Jun 2008, 17:44
Before I make any stupid comments, a question?

Do all present-day Wx radars now just use a pencil beam scanning in a single plane, or are there still "spoiled-beam" and GM type modes?

Apologies to ppppilot and ITCZ:
I've downloaded the pdf's , but I haven't read them yet.

CJ

Centaurus
25th Jun 2008, 12:55
CB tops may show little, if any, return...but turbulence can be severe.


At high altitude cruise it is a good idea to select maximum gain (if available on your specific radar installation) and this gives you an increase of 3881 percent power (Collins WXR 700X Pilots' Guide) above the AUTO gain. This increase in radar power will often show up CB tops as a small echo whereas nothing will show up on AUTO. Once you pick up this tiny echo, you can adjust gain and tilt to suit closer interpretation.

Flagon
25th Jun 2008, 13:23
Pointing it up us useless. - no. Not useless! Significant weather (and I assume you are looking to avoid turbulence and not just rain?) will have a significant 'footprint' above you on base leg. It is unlikely you will find any 'nasties' at 3000' that do not have higher activity.

My handling is like Centaurus and several others here - max gain at high level, scanner down to get ground returns at 80nm and occasionally sweep up and down a bit to check. (Most important to check lower levels as pantload said). Gain reducing as I descend to be at 'auto' below 5000' and scanner angle below 5000 at 5'ish. Sometimes 8 for departure where there is terrain.

That has worked extremely reliably over many years. Radar teaching is sadly neglected by airlines and it not unusual to find an F/O scanning low earth orbit for CB's for several hours on a cavok day:)

FullWings
25th Jun 2008, 14:21
Seconded about pointing it up on approach... If you don't, you get a mix of weather and ground clutter. Sometimes it's worth tilting it up to max. (15degs or more) because that's where down/micro-bursts are going to be coming from.

Even with the radar significantly pointing up, you are still going to see severe stuff far enough ahead to be able to avoid it. The same can't be said of a screen full of pretty colours from ground returns. :ooh:

ray cosmic
25th Jun 2008, 16:25
Radar teaching is sadly neglected by airlines and it not unusual to find an F/O scanning low earth orbit for CB's for several hours on a cavok day:)
SO true.
Good thread.:ok:

stator vane
25th Jun 2008, 20:49
circa 1992--i do believe i read in a United Airlines pamphlet-we did our training with them in Denver-- 6 degrees nose up for takeoff.

that is what i have used since i really haven't seen much else until this thread.

when i have the time, if it does appear very busy in the way of weather returns, i will run it up and down to get more information.

also, if new to an area, even when it is cavok, it is good to turn it on, so that you will become familiar with the returns that might be from buildings or terrain in the area. waiting for poor vis or extreme weather, before turning it on is too late.