Xponder control

[VNee]

Question from SLF but nevertheless an EE who flies a fair bit.
Hopefully, my question is technical enough to be posted here:

Wasn't a recommendation from the 9/11 commission to remove the
ability to switch off transponders from the flight deck? I understand
the need to prevent squawking on the ground but that could be easily
controlled by airspeed or the WoW signal. Additionally, is there a need
for pilots to control Mode S to mode C in certain countries or situations?

This is naturally brought to mind with the MH370 tragedy.

TIA to those who shed some light on this. Apologies if this has
been answered before and I missed it.

[oceancrosser]

I think the press and industry outsiders are putting far too much weight into the transponder issue. Once you are out of radar coverage, only the TCAS/ACAS/ADS-B (which requires being in range from a ground station) functions of the unit is of any value.

[CanadianAirbusPilot]

It is a good decision. Fact of the matter is when designing airplanes they are usually designed as simplistic as possible and not to take into consider every what if scenario.

I know the big jets don't really ever in formation very often (although I have seen a few cool pics from South African :ok:) but when flying in formation only the lead would have their transponder on.

In the event of an engine failure we turn the TA/RA mode to just TA so you still produce mode C just won't have an RA. It's probably simpler to design a transponder that is fully controlled by us rather than hooking it into other systems (like AS or WOW switches etc..)

Perhaps when the results of this mystery is known insurance companies may want a GPS tracking option on all airplanes? Hard to say.. Transponders only work if they are close enough to a secondary radar facility.

[VNee]

I understand that squawking would not have prevented/solved MH370 and
requires RF range but I thought that this recommendation had been adopted
by the industry being fairly simple+cheap to implement and having potential to
help in some situations.

Never considered formation flying (!) - Thanks for the tidbit.

[Denti]

Transponders are already hooked in the air ground logic and use it to set the "on ground" flag if the aircraft thinks it is on the ground. Which leads to very surprising issues if the A/G logic malfunctions and the plane takes off. Not only will there be issues with the gear, pressurization, and FMC logic, the transponder will transmit the ground flag as well which means that ATC will not correctly display it.

Anyway, as said above even transponders malfunction and sometimes need to be switched off without leaving the seat, finding the right CB and pulling it. The only thing on my small boeing flightdeck i can't switch off in any way is the ISFD, and since that contains its own battery pack it will merrily burn up without any chance to switch off electric energy...

[hvogt]

Wasn't a recommendation from the 9/11 commission to remove the ability to switch off transponders from the flight deck?Never heard of such a recommendation. Do you have a reference?

[VNee]

Hovgt wrote:
Never heard of such a recommendation. Do you have a reference? I cannot find a reference either so perhaps it was just discussed at one
point and I confused it for a recommendation. Thanks for clearing this up.

[TypeIV]

Well, someone who knows what he/she is doing can easily pull the affected CB or cut the power to the bus.

Hotwiring unnecessary stuff to the battery for this reason might not be a very good idea...

[Cough]

Say a fault develops in the transponder system, it can send out erroneous alt information. Say the mode C readout bounces up and down as a result of a fault, multiple aircraft would receive spurious and false TCAS alerts, affecting their safety.

As a result, flight crew can turn it off.

What I would like to see though, is the ability for ground authorities to be able to remotely activate the ELT...