Weather Radar on standby while taxying
 

I was taught many years ago never to put a serviceable weather radar to OFF while taxying as the antenna may get damaged due to the stabaliser being switched off. I always preach and practise this but I cannot find it in any literature . Googling doesn't help either! Does anyone of here know the source of this information( this was told to me by Eurocopter instructors). Nowadays we have to standby on the answers just in case some pilots like to switch off most non esseessential equipments after landing instead of waiting for the shutdown checks.

bouncy radar
 

I remember being told this a very long time ago. I believe that whilst the radar was off and the scanner was not sweeping the antenna would bounce up and down on the same place on the rack and wear it. I think it was an old wives tale.

Is there ever a need to put the radar to the OFF position given the potential of damage during taxi, even if not actually that likely, far outweighing the pitfall, which I can't think of. Also it means the radar is powered up and initialised should one need to get airborne in a hurry and enter IMC.... Just a thought.

I cannot speak for your particular radar, but the ubiquitous E190/290 used in C130, Jetstream, Dominie and lots of other UK military FW aircraft had a notoriously fragile scanner gearbox. GB casings cracked with monotonous regularly. In the horizontal plane, much depends on the scanner controller and how hard it is allowed to bang against the end stops. In the vertical plane, as bellboy says, it may depend on the yoke. I'd phone the radar manufacturer. They'll have installation and use instructions specific to aircraft types.

I was advised to do this years ago, and leave the radar on standby.

Being of a curious nature, I've opened up the nose bay and seen first hand what happens to the radar scanner plate when the aircraft is de-powered from the standby setting; it gently drops onto the lower extremity of it's travel. Having then checked how easy it is to move it in the vertical sense when unpowered, I'm sure it would "bounce" off the bottom stop during ground taxying.

(Our maintenance company also power up the aircraft gyros before towing it, or, I believe, alternatively wait thirty minutes after they were last switched off, so they are fully wound down; I str that one's a maintenance manual requirement).

That is certainly what I was taught on the AS332L, not sure if newer radar arrays have the same pitfall but I shall have a look at the 225 when I get to work.

Si

I also put the radar on standby when I do ground runs, basically, when ever the blades are turning, I put the radar on standby. This was also beaten into my years ago during my training on the gold ol Mk1 Super Puma and has been backed up by engineering. It saves damaging the gyro gimbal bearings.

ITI

I think this is a bit of an old wives tale, possibly origination from "olden days" when maybe it was a problem.

Quote from the Telephonics RDR1600 Pilot Handbook;

The design of the system is such that full operation is possible
approximately two minutes after turn-on. Therefore, the pilot may
choose to leave the function switch in OFF, rather than STBY, if no
significant weather is in the immediate area of the aircraft. The life
of the magnetron transmitting tube will be extended by leaving the
system “OFF” when possible. This, in turn, will reduce the cost of
maintenance.

I enquired of two senior, highly experienced avionics engineers in my last company and neither of them had ever heard of radar gimbal bearings failing. They did not think the radar would be damaged by switching it off.

In my case, the subject came up because we had a couple of aircraft which suffered from r/t interference from the radar on a particular VHF frequency and the short term cure was to switch the radar off.

Radar in Stby during taxi
 

Here's my 2 cents worth.

Many years ago in a previous life on fixed wing using older generation radar antennas which relied on physical movement of antenna to scan, it was indeed a requirement to put the Radars in Stby whenever taxiing.

This was to ensure that the antenna was "parked" i.e. held in a fixed position by the gimbal/gyro stabilisation system under power. This did indeed prevent the "bouncing" of the antenna and damage of the very sensitive bearing/gymbal system if not powered up.

With the newer generation of fixed antenna and phased array system of beam scanning, the antenna is generally fixed and the beam is scanned electronically i.e. stuff-all moving parts.

I think you will find this is what is meant when system manufacturers say that "The design" doesn't require power on during ground movement……..

I suspect your earlier AS332's and other helicopters may well have also had ealeir radar's with antennas which physically moved to create the beam scan….hence the teaching of "stby" mode during any movement - in order to reduce potential damage to antenna bearing systems.

As a guideline, I would suggest any radar that has a phased array electronically controlled beam scan would not require power-on/Stby mode selected during aircraft movement. The older generation radars with a physically moving scanning antenna would probably be beneficial to have power applied to stabilise or lock the antenna in a fixed position to avoid potential damage to the antenna bearing/gymbal system….and improve system longevity.


For what its worth……

cheers

In addition to this-one should consider possible damage to people walking around while taxiing...

Usually, the helicopters i have flown, there was a "weight on wheel" switch installed that switched the radar to stdby as long as you were taxiing.

On bad weather, the procedures were to line up on the runway, do the checks, and switch the "WoW-override" on to have the radar ready before departure..