I read the above somewhere but also I am aware of counter-examples.
My TB20GT (2002) has an EDM700 which was installed by Socata as primary (the GT had no CHT gauge) but it comes on with the AVIONICS MASTER. That seems sensible because it provides the instrument with protection from starter motor inductive spikes.
Can anyone come up with a reference for such a requirement, or maybe mention other counter examples?
I thought the main idea with a master switch was to be able to turn things off, to pull the plug so to speak. If it turns stuff on or not should be irrelevant.
Is it required as part of the TC? A CHT/EGT isn’t a required instrument unless it’s part of the TC AFAIK so I can’t see how it’s required to be switched by any specific switch.
For any aircraft which wants an FAA TC, you have FAR 91.205:
So, correct, no CHT gauge is needed by the certification authority. But a number of the items above (e.g. tachometer) are delivered by instruments which have an STC as “primary”.
I have no idea where to find the corresponding EASA table.
Peter wrote:
Manifold pressure gauge for each altitude engine.
What’s an “altitude engine”? Turbo/supercharged?
I have an electronic tach and it was installed on the main bus. Comes on with the master. I suspect that was mandatory, but can’t quote any reference to back it up. N-reg.
The tachometer obviously must come on immediately, not after the avionics master. One needs it to set the RPM for idle, etc.
Would anybody know where the above equipment lists might be? @wigglyamp?
I have the Feb 2006 CD MM but nothing comes up on a search
Interesting that none of the certification specialists here found it (I believe wigglyamp has left) but eventually I did after a lot of digging.
The mandatory equipment is listed in the POH under Weight & Balance!
At the very end of the list is this
which shows that not only is a CHT gauge not mandatory on the TB20GT (“post Mod 151” is what they call the GT) but the EDM700 is not mandatory either.
The tachometer is mandatory (R = required equipment) so a replacement needs to be either PMA or STCd as Primary. But the EDM700 is optional, which might surprise a number of avionics shops who have installed other instruments, saying a Primary STC is required.
The remaining question is what happens when the “Standard equipment” Alcor CHT/EGT gauge is removed, which was done by Socata. I believe it looked something like this
It still doesn’t look like the replacement needs a Primary STC.
It would be interesting to see the corresponding POH page from a TB21 POH. It should say the above gauge is (R) i.e. Required equipment i.e. mandatory.
The other useful thing about that POH section is that it lists a lot of OEM part numbers, not just the anonymised Socata ones