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Instruments certified as PRIMARY - do they need to come ON with the electrics MASTER switch?

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?

Administrator
Shoreham EGKA, United Kingdom

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.

The elephant is the circulation
ENVA ENOP ENMO, Norway

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.

Andreas IOM

For any aircraft which wants an FAA TC, you have FAR 91.205:

  • Airspeed indicator.
  • Altimeter.
  • Magnetic direction indicator.
  • Tachometer for each engine.
  • Oil pressure gauge for each engine using pressure system.
  • Temperature gauge for each liquid-cooled engine.
  • Oil temperature gauge for each air-cooled engine.
  • Manifold pressure gauge for each altitude engine.
  • Fuel gauge indicating the quantity of fuel in each tank.
  • Landing gear position indicator, if the aircraft has a retractable landing gear.
  • For small civil airplanes certificated after March 11, 1996, in accordance with part 23 of this chapter, an approved aviation red or aviation white anticollision light system. In the event of failure of any light of the anticollision light system, operation of the aircraft may continue to a location where repairs or replacement can be made.
  • If the aircraft is operated for hire over water and beyond power-off gliding distance from shore, approved flotation gear readily available to each occupant and, unless the aircraft is operating under part 121 of this subchapter, at least one pyrotechnic signaling device. As used in this section, “shore” means that area of the land adjacent to the water which is above the high water mark and excludes land areas which are intermittently under water.
  • An approved safety belt with an approved metal-to-metal latching device for each occupant 2 years of age or older.
  • For small civil airplanes manufactured after July 18, 1978, an approved shoulder harness for each front seat. The shoulder harness must be designed to protect the occupant from serious head injury when the occupant experiences the ultimate inertia forces specified in § 23.561(b)(2) of this chapter. Each shoulder harness installed at a flight crewmember station must permit the crewmember, when seated and with the safety belt and shoulder harness fastened, to perform all functions necessary for flight operations. For purposes of this paragraph -
    (i) The date of manufacture of an airplane is the date the inspection acceptance records reflect that the airplane is complete and meets the FAA-approved type design data; and
    (ii) A front seat is a seat located at a flight crewmember station or any seat located alongside such a seat.
  • An emergency locator transmitter, if required by § 91.207.
  • For normal, utility, and acrobatic category airplanes with a seating configuration, excluding pilot seats, of 9 or less, manufactured after December 12, 1986, a shoulder harness for -
    (i) Each front seat that meets the requirements of § 23.785 (g) and (h) of this chapter in effect on December 12, 1985;
    (ii) Each additional seat that meets the requirements of § 23.785(g) of this chapter in effect on December 12, 1985.
  • For rotorcraft manufactured after September 16, 1992, a shoulder harness for each seat that meets the requirements of § 27.2 or § 29.2 of this chapter in effect on September 16, 1991

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.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Manifold pressure gauge for each altitude engine.

What’s an “altitude engine”? Turbo/supercharged?

ESKC (Uppsala/Sundbro), Sweden

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.

LSZK, Switzerland

The tachometer obviously must come on immediately, not after the avionics master. One needs it to set the RPM for idle, etc.

Administrator
Shoreham EGKA, United Kingdom

OK; more digging. The TB20 TCDS lists required equipment

I don’t know where this equipment list can be found.

Administrator
Shoreham EGKA, United Kingdom

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

Administrator
Shoreham EGKA, United Kingdom

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

Administrator
Shoreham EGKA, United Kingdom
19 Posts
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