B738 WX radar activation during T/O config check
 

Hi guys and girls,

Could anyone offer a technical insight into this part of FCOM?

FCOM 2 Warning Systems - "The wx radar automatically begins scanning for windshear when:
Thrust levers set for takeoff, even if engine is off or IRS not aligned... ...Alerts are available approximately 12 seconds after wx radar begins scanning for windshear..."

It was part of my previous company SOP to do T/O config check twice on stand so I would like someone to tell me that I wasn't x-raying people on the ground...

Only if the Wx radar is selected ON via the main Wx radar panel & the EFIS control panel. It is most common to activate the Wx radar via EFIS panel when lining up for takeoff. I assume you do not have Wx radar pin while parked.

Well that was what I thought up till now but the FCOM clearly states that WX goes on regardles. The info I have is that Boeing implemented this feature to provide predictive windshear alert on T/O even when you forget to put the WX radar on. It apparently activates with thrust lever beyond certain Thrust lever angle.

Noox, you are correct the radar activates for predictive wind shear even if it isn't selected on and it uses the same switch as the config warning.

For that reason my old airline stopped doing the config check warning check when we transitioned from classics to NG's.

My understanding is most modern radars do not have a danger area like the 20 feet (?) limit on older systems. The October 1994 edition of the Collins WXR-700X Weather radar systems Pilots Guide on page 33 has a Note stating: The average radiated power density of the Collins WXR-700X is significantly less than the 10,W/cm2 allowable for limiting the exposure of rf energy to humans as noted in FAA Advisory Circular, number 20-68B, dated August 1980. The WXR-700X does not require the use of dummy load when operated on the ground.

I understand that means if there is a danger area it is about two centimetres in front of the dish? I recall that figure from a technical document a long time ago but don't know which one so treat with caution.

TWICE? I don't fly the 737, but what on earth for? It tests, it works. The test only proves it worked when you tested, it's not predictive.

Once per T/L maybe?

The airline (blue and yellow) was afraid of us taking off not configured. You would test it once during preliminary preflight flow and second time during before start checklist. Most of the times the tug driver was sitting in front of the WX radar:sad: ...

Don't know the 737, but why would you do the config test on stand before the flaps are set?
On the A300 we did the config test at line up as it also included parking brake as well as flaps, slats, trims, etc.

Company SOP to test the operation of config warning. If you remember the Spanair accident where they took off not configured without them knowing that (T/O config not working). This SOP should prevent it (or at least tell you that T/O warning is not working). The thing is when you do it this way, you always have people around the A/C and they get x-rayed.

you always have people around the A/C and they get x-rayed.

Are you telling me Hi Viz jackets will not save you. I thought they were bullet proof, flotation devices, anti radiation, anti hunger & thirst, and even let you think you are God and in charge.

Now we find they have a weakness after all and not the eternal saviour we were led to believe. I'm aghast with shock horror.

RAT 5,

I don't really get the added value of you posts...

1) During preliminary flight deck preparation the system is checked for functionality, as you KNOW the sound MUST sound as you are on stand, parking brake set, flaps up.

2) After having configured the aircraft for departure, prior to taxi or in freezing conditions after configuration of flaps prior to lineup, the config check is done to ensure correct configuration for departure.

3) Any subsequent takeoff config during departure on the runway means step 2 has been missed and thus aircraft is not properly configured and requires an RTO to establish the reason

In the outfit described a return to stand is mandatory after a config on the runway, previous steps prevent this from happening IF following SOPs.

I get it.
We did the test with the pre flight check prior to first flight on any particular aircraft, not at each turn round.
Each company has their own SOPs.

And some of those SOPs lead to weather radar activation at an inappropriate time.

RAT5 - thanks for making me laugh.

X-rays? Since when do radars use x-rays? All the ones I have used are X-band microwaves: 8 - 12 GHz.

X-rays are quite a different thing, 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz). X-rays are used for stuff like medical imaging or pipeline inspection.