Instrument Flight Deck Check

Because before any flight involving aircraft control by instrument reference, you must check all instruments and their sources of power for proper operation (IFH ch. 5). It's a small slice of preflight time, but it's your only chance to catch a lazy gyro, a mis-reading altimeter, or a lapsed inspection before the airplane is your only horizon. The task is really two checks: the paperwork (is this airplane legally IFR-airworthy today?) and the instruments themselves (are they actually working?).

Everything from day VFR (the ATOMATOFLAMES list you know from the private), plus night VFR equipment if the flight is at night, plus the GRABCARD items — generator/alternator, two-way radio and navigation equipment suitable for the route, sensitive altimeter, slip-skid indicator, clock with seconds, attitude indicator, rate-of-turn indicator, and directional gyro (91.205(d)). Note "suitable for the route" is doing real work: the required nav equipment depends on what you filed.

On top of the annual (and 100-hour, if the aircraft is operated for hire) you already track:

• VOR check — every 30 days if using VOR for IFR navigation (91.171)
• Altimeter and static system test — within the preceding 24 calendar months (91.411; IFH ch. 5, ch. 10)
• Transponder test — within the preceding 24 calendar months (91.413; IFH ch. 10) — strictly this one isn't IFR-specific: it applies to any use of the transponder, VFR or IFR (91.215(c))

The altimeter/static and transponder tests live in the maintenance records; the VOR check lives in the aircraft log "or other record" you keep (91.171(d)).

The methods are in preference order: use a test signal or surface checkpoint if available before resorting to airborne checks (91.171(b)–(c)).

The person making the check enters date, place, bearing error and signs the aircraft log or other record. If a repair station's radiated test signal was used, the repair station also makes an entry certifying the transmitted bearing and date (91.171(d)). Four items — the examiner loves asking for all four.

1. Tune the VOT frequency — published in the Chart Supplement — and listen for the series of dots or the continuous 1020-Hz tone
2. Course selector to 0° — CDI centers with a FROM indication
3. Course selector to 180° — CDI centers with a TO indication

("Cessna 182": 0-FROM, 180-TO.) To measure the exact error, center the needle and note the degrees off 0° or 180°; more than 4° and the receiver is out of tolerance. An RMI should indicate 180° regardless of OBS setting (IPH ch. 2; 91.171(b)(1)).

Set the current altimeter setting; the altimeter should indicate within 75 feet of the field elevation. Beyond that, the altimeter's accuracy is questionable and the instrument goes to a repair station — but first recheck in the run-up area, since ramp elevation can differ meaningfully from published field elevation. With no altimeter setting available, set the published field elevation for the preflight check (IFH ch. 5).

• Attitude indicator — erects within about 5 minutes (normally 2–3); horizon bar stays level taxiing straight and tips no more than 5° in taxi turns, or the instrument is unreliable
• Heading indicator — set to the compass after spin-up; before takeoff it should agree with the known runway or taxiway heading within 5°
• Turn coordinator — in taxi turns, miniature aircraft shows the turn direction and the ball swings freely opposite the turn

Listen at power-up too: hesitation or unusual noises as the gyros spin up gets investigated before flight (IFH ch. 5).

• Database current — within its 28-day cycle and supporting the operation; required for IFR GPS (IFH ch. 9)
• Position initialized correctly, and the active flight plan cross-checked against the charts (IPH ch. 2)
• GPS NOTAMs and WAAS status reviewed; RAIM prediction obtained from the receiver or FSS for non-WAAS operations (IFH ch. 9)

Charts count too: en route charts revise every 56 days — an out-of-date chart or database is a Task II.C risk element in itself (IFH ch. 1).

Same ladder as VFR — MEL if one exists; otherwise the item must not be required by the type certificate/equipment list or KOEL, by 91.205, by an AD, or for the operation, then deactivate or remove, placard "Inoperative", record it, and a pilot or mechanic determines it's safe (91.213(d)). The IFR difference: "the operation" now sweeps in 91.205(d) — a dead attitude indicator, clock, or alternator that might placard away for day VFR grounds the airplane for IFR. And a broken transponder or ADS-B can still fly to a repair point, but only with the ATC authorization of 91.215(d)/91.225(g).

• Walk-around — pitot cover off, tube unobstructed; static ports clear and nothing near them disturbing airflow; antennas in good condition
• Records — altimeter/static system tested within 24 calendar months; ELT battery replacement date in the maintenance record
• Paperwork — Chart Supplement and NOTAMs for every NAVAID you'll use; charts and plates for departure, en route, destination, alternate
• Panel — radios off before start; altimeter set and indicating field elevation; magnetic compass full of fluid with a current correction card; clock set and running; alternate static valve opens and closes fully; pitot heat verified by ammeter draw or the POH method (IFH ch. 5)

• Listen to the gyros spin up — no hesitation or odd noises
• Suction gauge (or electrical indicators) — power source appropriate for that aircraft's instruments
• Magnetic compass — card swings freely, bowl full, compare against a known heading while stopped or taxiing straight; note the correction for the runway heading
• Heading indicator — allow about 5 minutes for spin-up, set to the compass; check slaving on a slaved system
• Attitude indicator — erects and holds the correct attitude
• Altimeter — within 75 feet of field elevation
• VSI — reading zero (tap the panel gently if not)
• Radios checked and set; deice/anti-ice checked for operation (IFH ch. 5)

Not necessarily an IFR no-go — the VSI is not a 91.205(d) required instrument. The IFH's ground check expects zero (tap gently first); a stuck non-zero indication is the kind of "possible defect" this task exists to catch, so treat the indicated offset as the instrument's new zero reference in flight, and consider 91.213 handling if it's genuinely failed. Contrast that with the sensitive altimeter, clock, or rate-of-turn indicator — those are GRABCARD items, and a defect there ends the IFR flight (91.205(d); IFH ch. 5).

At and above FL 240, if VOR navigation equipment is required for the route, the aircraft must also have approved DME or a suitable RNAV system. If it fails at or above FL 240, notify ATC immediately — then you may continue to the next airport of intended landing where repairs can be made (91.205(e)).

Not with GPS as your IFR navigation source — an updatable database supporting the operation is required for IFR GPS, and using GPS in place of DME/ADF explicitly requires a current database (IFH ch. 9). Your options are updating it before departure or planning the flight on ground-based navigation appropriate to the route (with the VOR check current, of course). This is IR.II.C.R2 in its purest form: outdated navigation data is an airworthiness problem for the operation, even when the airframe itself is pristine.