How can I check pitot static leak without a test box?

Question

More than once on the ramp, I've wished I could check an aeroplane's pitot-static system for leaks, but I didn't have the test box. I've since seen, in the FAA's handbook for checking homebuilts, a way of gently pressurizing a pitot system which is great - a length of medical tubing is all you need.

Does anyone know if a similarly simply elegant arrangement exists for the static system? I've tried a largish hypodermic syringe to check if the port was blocked, but the challenges are:

1. getting to sit tight on the static port, and
2. holding suction.

All suggestions welcome.

Answer 1

There are lots of challenges to testing a static system the way you describe.

First, you need something to fit over the static port (not too hard if it's a single fuselage port, slightly more difficult if it's two of them, and if it's on a mast like on some Piper aircraft you just lost a lot of "seal area" and made the task very difficult).
You can get around that with test kits by taking the static line(s) off & screwing the test kit directly to the plumbing, or by using a variety of adapters that come with the kits.

Second, you need to produce a known absolute pressure in the line and hold it for a given duration to check for leaks.
That's most of what those fancy boxes do - they bring the line to a given pressure altitude, and then you watch the altimeter and/or line pressure to see if it leaks air back into the system.

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All that said, if you're willing to deal with a really rough test, you can still do this with a syringe and some medical tubing. This RV-12 builder shows you how:

1. Attach a syringe to some surgical tubing.
2. Put some air-tight tape over your other static port (if applicable)
3. Put some modeling clay around the static port.
   DON'T get it in the hole - make kind of a cup around the hole.
4. Put the surgical tubing into the modeling clay and press the clay tight around the tube to seal the chamber over the static port.
5. Pull on the syringe until you "climb" to a convenient altitude.
6. Hold or lock the syringe in place and watch the altimeter to see how long it takes for air to leak into the system and lower your altitude.

This is nowhere near as precise as proper calibrated test equipment, but it should help you detect a gross leak in the static system.

Answer 2

The correct answer is that only approved equipment and procedures should be used. In a pressurized aircraft, a leak is rather easy to know you have. If you’re flying above cabin altitude and you have a leak inside the pressure vessel, your altimeter will read roughly cabin altitude and your respective airspeed indicator will read low.

In a smaller aircraft, there really isn’t a good way to know. Tapping into a line with a tee-fitting may prove good, but what about the disconnection of the tee fitting and the subsequent hookup of the aircraft lines? How do you “know” they are ok?

There is one trick that I have used as an A&P for hard to find leaks. The lines in most aircraft are stainless steel. Provided the respective endpoints are removed and capped (instruments, etc), I will hook dry nitrogen up to the static port and run it at 20-30 psi and listen for the hissing noises.

20-30 psi will not damage a stainless steel line or the fittings. The biggest risk is ensuring every instrument is removed as you could damage them.

Using anything other than dry nitrogen would be a mistake, though, as other gas with moisture could induce moisture into the system.

Answer 3

just plumb a test port into the static line ---A "T" for instance--- then block the static ports--use soft silicone tubing to fit over the T and suck gently until the altimeter reads about 2k above field elevation put tongue over tube very scientific now watch for drop in altitude after VVI goes to zero no more than 100 feet in a minute is acceptable see 4313.1B for this technique