2.5 The Instrument Flight Deck Check & Flight Control Verification

The Instrument Flight Deck Check & Flight Control Verification

Quick Answer: The instrument flight deck check exists to detect defects on the ground, where they cost nothing. Its four stages are (1) a pre-start documents, publications, and panel review; (2) a post-start power-source check — suction 4.5 to 5.5 in Hg, ammeter charging, annunciators out, AHRS/ADC aligned with no red X; (3) the taxi check, where a turn to the left must produce a left-banking turn coordinator with the ball to the right, a decreasing heading indicator that agrees with the magnetic compass, an erect attitude indicator, and motionless airspeed, altimeter, and vertical speed indications; and (4) a before-takeoff sweep of instrument settings, navigation sources, and flight controls free and correct with trim set and the autopilot disconnect verified.

Every other regulation in this chapter — 14 CFR § 91.205, § 91.213, § 91.411, § 91.171 — establishes what must be installed and inspected. The instrument flight deck check answers a different question: is it actually working right now, in this airplane, on this day? Once an aircraft enters cloud, the pilot has no external reference against which to test an instrument. A slowly precessing heading indicator, a vertical speed indicator that rests 200 feet per minute low, or an attitude indicator that never fully erected are all trivially detectable on the ramp and potentially fatal in IMC.

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Stage 1: Pre-Start Cockpit Review

Paperwork and Publications

Panel Walk (Left to Right)

Every instrument has a correct rest indication before the engine turns:

• Airspeed Indicator: Needle at or near zero, glass intact, markings legible.
• Attitude Indicator: Miniature aircraft adjustable, no obvious tilt, case secure.
• Altimeter: With the current local setting in the Kollsman window, the altimeter must indicate within ±75 feet of the surveyed field elevation. A larger error means the altimeter is questionable for IFR.
• Turn Coordinator: OFF flag in view (electrically powered, engine not running), inclinometer fluid full, ball centered on a level ramp.
• Heading Indicator: Card free to rotate with the caging/adjust knob, no obvious binding.
• Vertical Speed Indicator: Reads zero — or note the exact standing offset, because that offset must be applied to every in-flight reading.
• Magnetic Compass: Bowl full of fluid with no bubbles, card swings freely, and a legible compass correction card is installed.
• Clock: Installed, running, and displaying seconds, as required by 14 CFR § 91.205(d)(6).
• Alternate static source: Valve accessible from the seated position and the POH correction table located.

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Stage 2: After Engine Start — Power Sources and Avionics

This is where the two independent power supplies that keep an instrument panel alive get tested.

[!NOTE] Set the altimeter from a current source. Take the setting from ATIS, AWOS, ASOS, or clearance delivery — not from yesterday's value or from field elevation guessing. The ±75-foot tolerance is only meaningful when the setting itself is current.

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Stage 3: The Taxi Check (The Highest-Value Item)

Taxiing is the only opportunity to make the airplane turn on a known heading, at a known rate, with the ground visible. Announce it out loud — "turning left" and "turning right" — and check five instruments each way.

+-----------------------------------------------------------------------------+
|                  TAXI CHECK: TURNING LEFT (Northern Hemisphere)             |
|                                                                             |
|   INSTRUMENT              CORRECT INDICATION                                |
|   --------------------------------------------------------------------     |
|   Turn Coordinator        Miniature aircraft BANKS LEFT                     |
|   Inclinometer (Ball)     Ball swings RIGHT (to the OUTSIDE of the turn)    |
|   Heading Indicator       Heading DECREASES and agrees with the compass     |
|   Magnetic Compass        Card swings freely, indicates a LEFT turn         |
|   Attitude Indicator      Stays ERECT (no more than about 5 deg of error)   |
|   Airspeed Indicator      Remains at ZERO                                   |
|   Altimeter               Steady at field elevation                         |
|   Vertical Speed          Remains at ZERO                                   |
+-----------------------------------------------------------------------------+

Why the Ball Goes to the Outside

During a ground turn there is no bank and therefore no horizontal component of lift to balance centrifugal force. The ball is thrown to the outside of the turn — right ball in a left turn, left ball in a right turn. This is the reverse of a coordinated turn in flight and is exactly the indication the FAA expects a candidate to name.

Comparing Heading Indicator to Magnetic Compass

Set the heading indicator to the magnetic compass while stopped and straight, then confirm during the turn that both move in the same direction and arrive at approximately the same heading. A heading indicator that lags, sticks, or spins is a vacuum or gyro problem; a compass that sticks or reads backward is a fluid or magnetization problem.

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Stage 4: Run-Up, Flight Controls, and Before Takeoff

Flight Control Systems

The ACS treats flight control systems as instrument-flight knowledge in its own right, because an out-of-trim or restricted control system in IMC destroys the pilot's ability to fly precisely.

1. Controls free and correct through full travel in all three axes — visually confirm the surfaces move in the correct direction, not just that the yoke moves.
2. Trim set to the takeoff position for the loaded center of gravity; verify the trim indicator and the physical trim tab agree.
3. Electric trim runs at the expected rate in both directions and stops instantly when the trim interrupt is pressed.
4. Autopilot preflight test completes without fault; then verify the AP disconnect on the yoke actually releases the servos. An autopilot that cannot be switched off is a hazard, not a workload reducer.
5. Flap operation symmetric and full travel, with the indicator matching the actual setting.

Final Instrument Sweep Before Takeoff

• Heading indicator aligned with the magnetic compass and cross-checked against the assigned runway heading.
• Attitude indicator erect and level with the miniature aircraft set for the seated eye position.
• Altimeter on the current setting; note field elevation for the departure.
• Navigation sources tuned, identified by Morse code, correct CDI source selected, and the approach or departure procedure loaded.
• Clock or timer available for the departure and any timed procedure.
• Transponder to ALT and ADS-B active.

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Detecting Defects: The Underlying Skill

A checklist tells a pilot what to look at; the instrument flight deck check is about knowing what right looks like so the wrong thing announces itself:

• Cross-check redundant sources. Standby attitude indicator against the PFD; heading indicator against the magnetic compass; GPS groundspeed against airspeed and known wind.
• Distrust "it will settle in flight." Gyros that are slow to erect, needles that hang, and annunciators that flicker do not fix themselves in cloud.
• Treat any red X, flag, or failed self-test as a 14 CFR § 91.213 decision, not a judgment call about how far the flight is going.
• Log what you find. A discrepancy noticed and not written up is a discrepancy the next pilot will discover in IMC.