Radar Altimeter Standby
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Why is the radar altimeter placed in standby during ramp start, instead of just leaving it off?
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Because it needs some time to be operational. For takeoff you definately want the radar altimeter working, so by putting it in standby during rampstart, you ensure that it is ready for use when taking off.
cheers
Magic -
Cos it emits radar waves which could do a good job of sterilising the EOR operatives - leave on standby until you are lined up for take-off and doing your final checks.
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It’s a magnetron or whatever is the heart of radars and it needs to get hot. It also has some built-in test and monitoring so it’s good to know it works (communicates on bus, etc) as much as possible as early as possible before actually doing any emission.
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Cos it emits radar waves which could do a good job of sterilising the EOR operatives - leave on standby until you are lined up for take-off and doing your final checks.
This is why. Not a good idea to burn the ground chief.
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If you read the question carefully it asks why use standby instead of off not standby instead of on.
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@jc1:
Why is the radar altimeter placed in standby during ramp start, instead of just leaving it off?
Same reason as going to emissions “silent” mode before refueling.
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If you read the question carefully it asks why use standby instead of off not standby instead of on.
I didn’t want to deny you
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@jc1:
Why is the radar altimeter placed in standby during ramp start, instead of just leaving it off?
Depends on which checklist you use as to which position you are directed to put it in.
The USAF version just tells you to turn it straight on, no waiting in standby. HAF version tells you to go to standby, and I guess this is the checklist that the BMS ones were based on.
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In which case, why not just leave it off?
As Frederf said earlier, it needs to warm up. If you leave it off until you’re ready to go it won’t be immediately available when you do need it.
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Thanks for all the advice. To test your advice at the ramp start runway, I left the radar altimeter switch off, put my altitude switch on radar, took off, switched on the radar alt and found out radar needed about 10-11 seconds for radar altitude to get active.
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@jc1:
Thanks for all the advice. To test your advice at the ramp start runway, I left the radar altimeter switch off, put my altitude switch on radar, took off, switched on the radar alt and found out radar needed about 10-11 seconds for radar altitude to get active.
… which is the blink of an eye in the grand scheme of things. I guess then (in relation to BMS) it can come down to personal preference? In the real world, it would be set IAW squadron SOP.
@Agave_Blue - well, yes and no. My understanding is you would place the switch to standby during start-up for the reason it will be warmed up and not emitting thus achieving two goals - immediate availability when required, and not cooking the crew chief. Going silent at air refuel prevents you cooking the boom operator. This, of course, might be complete pony…!
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I always just turn it on right away. But then again I also go to quiet during AAR, not silent…
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If the (internal) RALT BIT fails, you cannot fly the bird / mission (not allowed), so following SOP’s and logical thinking of how simple is and how it works, it’s not a good idea to discover its fail on the runway.
Same logic with other flight-critical systems that should be checked immediately after engine start, so if anything is a no-go you shutdown the jet and move to the alternative standby.
- Fire/Overheat line circuits test
- Engine SEC
- EPU check
- FLCS BIT
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This is why. Not a good idea to burn the ground chief.
Not even part of a Dos Gringos song so it must be quite dangerous;) How does the same apply for the FCR? Am I missing the radar-snooze in my ramp-procedure?
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Depending the mission, you can SAFELY fly without the FCR. Flight will turn unsafe thus instructed to abort if other systems (radios, ins/egi) are also failed in the ground.
FCR performs SelfBIT upon power-up. No emission are transmitted there dangerous to the ground crew. I’ve then seen SOP’s where radar antenna should be commanded to move looking upper gimbals when on ground, either with the radar is “ready” mode where WoW is just preventing it to emit or in STBY mode.
BUT, WoW override switch placed in the intake side panel is just a simple switch right? Cannot this also fail, sort-circuit, or accidentally moved to the wrong position in the ground? Would be bad for the ppl in front of the bird…
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Depending the mission, you can SAFELY fly without the FCR. Flight will turn unsafe thus instructed to abort if other systems (radios, ins/egi) are also failed in the ground.
FCR performs SelfBIT upon power-up. No emission are transmitted there dangerous to the ground crew. I’ve then seen SOP’s where radar antenna should be commanded to move looking upper gimbals when on ground, either with the radar is “ready” mode where WoW is just preventing it to emit or in STBY mode.
BUT, WoW override switch placed in the intake side panel is just a simple switch right? Cannot this also fail, sort-circuit, or accidentally moved to the wrong position in the ground? Would be bad for the ppl in front of the bird…
BAF SOP dictates FCR OVRD till 500ft AGL altitude, IIRC.