Instruments and the pitot-static system

Six procedures.

Procedure 1 — Static system leak test (S1, K19, R5)

Regulated work. Read part 43 appendix E before you start, every time.

1. Confirm the test is required and why — interval, or maintenance that disturbed the system.
2. Isolate or protect instruments the procedure requires you to.
3. Connect the test set to the static ports, sealing them per the procedure.
4. Apply vacuum slowly to the specified altitude equivalent — never exceed instrument ranges.
5. Hold, and observe the leak rate over the specified time.
6. Compare against the tolerance in appendix E.
7. Release slowly.
8. Record: the test, the method, the result, the date, and the entry under GEN-I Procedures Procedure 6.

Check — read the tolerance out of appendix E and say it before you start. A test whose pass criterion you cannot state is not a test.

Failure — applying pressure to the static system, or vacuum to the pitot. Reversed, it over-ranges the instruments in the direction they cannot take, and all three are damaged with no outward sign (AF-H Concepts §2).

Procedure 2 — Remove and install an instrument (S2)

1. De-energize and, where the instrument is pneumatic, isolate the lines.
2. Handle gyroscopic instruments as fragile, in packaging, without shock (AF-H Concepts §3).
3. Disconnect electrical and pneumatic connections, capping the lines immediately.
4. Remove mounting hardware, supporting the instrument.
5. Install the replacement: confirm the part number is correct for the aircraft, fit mounting hardware, reconnect, torque per the manual.
6. Check the range markings are correct for this aircraft (Procedure 3).
7. Check bonding where the installation requires it.
8. Functional check, and leak check where the system was opened.

Check — cap every line as it comes off. An open static line collects debris and moisture, and the next leak check will fail for a reason you introduced.

Procedure 3 — Install and check range markings (S3, S5)

1. Get the values from the aircraft's TCDS, not from the instrument and not from another aircraft (GEN-I Procedures Procedure 1).
2. Confirm the instrument's scale matches the values — the same limitation on a different scale sits in a different place.
3. Apply markings by the approved method, on the glass or the dial as specified.
4. Apply a slippage mark across the glass and the case.
5. Check alignment against the dial.

Check — the slippage mark is the check, and it is permanent. A marking that has rotated is worse than none, because it looks authoritative (AF-H Concepts §5).

Procedure 4 — Inspect a magnetic compass (S6)

1. Check the fluid level — a bubble is a finding.
2. Check for discoloration, leakage, and card freedom — the card must swing freely and settle.
3. Check the compensating screws are secure and the correction card is present, legible and for this aircraft.
4. Check mounting security and that no ferrous or magnetic item has been placed nearby.

Check — the correction card must match the aircraft and its current configuration. A card from before an avionics installation is a card for a different magnetic environment.

Procedure 5 — Vacuum system: filter, then regulator (S10, S11)

Order matters (AF-H Concepts §4).

1. Inspect the filter first. Replace at the specified interval or if restricted.
2. Check the system for leaks — hoses, connections, and instrument case seals.
3. Only then measure vacuum at the specified point, with the engine at the specified RPM.
4. Adjust the regulator to the specified value.
5. Recheck after adjustment, and check gyro erection times.

Check — if you had to move the regulator a long way, ask why. A large adjustment usually means a restriction or a leak that you have just compensated for rather than fixed.

Procedure 6 — Inspect the alternate static source (S12)

1. Confirm the selector operates and reaches both positions positively.
2. Check the alternate port is clear and correctly located.
3. Confirm the placard is present and legible.
4. Include the alternate position in the leak check where the procedure requires it.

Check — an alternate static source that has never been tested is not a system, it is a control. It is only useful if it works when the primary is blocked, and that is exactly when nobody will be able to test it.

The checks, collected

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