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Sealed toggle switches

One thing which came up on a recent project was the use of fully sealed switches.

Virtually all light GA planes use non sealed switches, which can ignite a fuel leak if operated in the presence of a vapour concentration in the right % range.

These are cheap - under €2 for a little one (which is basically what got fitted with my £12k TCAS system), or say €10-30 for one with some paperwork.

The sealed ones don't necessarily cost a lot more - example - but that one is not necessarily sealed both front and back.

The first two toggle switches here - APEM are sealed at both ends, and cost €50-100. The 2nd one down (the black one) is the best, and really feels like it's worth the money.

This is another one, used on high-end American aircraft (APEM is French so they won't use it).

Smaller (1/4" hole) versions are not so common but this is one example - again not cheap.

Same considerations apply to the PTT switch, which you will definitely want to use if there is a fuel leak... again, the cheap ones are open. Proper ones here.

Just in case somebody is doing some panel building; now you can hassle your avionics shop

Administrator
Shoreham EGKA, United Kingdom

Virtually all light GA planes ...

You can probably extend this to "virtually all planes"..

... use non sealed switches, which can ignite a fuel leak if operated in the presence of a vapour concentration in the right % range.

This concern of yours falls in my "if you are scared of flying - don't fly" category ;-) Firstly, you can very well smell dangerous fuel vapour concentrations and secondly, many factory installed switches like the gear and flap switches as well as some relays are not of the sealed type either. Some battery relays I've seen are completely open! If you are concerned about vapour and gas concentrations, better invest your money in a good carbon monoxide detector.

But there's actually one good reason for installing sealed switches: Dust and moisture won't get inside so easily making the switch more reliable.

EDDS - Stuttgart

You can probably extend this to "virtually all planes"..

The TBM uses the APEM switches, but I very much agree about the copious numbers of non-sealed relays elsewhere...

Certainly you can smell fuel vapour long before it gets ignitable, but in-flight you don't have many options.

I think that, for the relatively small cost per-job, using sealed switches and sealed relays is worth doing.

Administrator
Shoreham EGKA, United Kingdom
3 Posts
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