Common errors

Instrument straight-and-level errors split into three families: scan failures (omitting instruments, fixating, breaking the cycle), interpretation errors (correcting the wrong instrument), and control discipline errors (chasing without trimming). The seven below cover the common faults.

1. Fixating on the AI

What it looks like: the pilot's eyes lock on the AI; small attitude adjustments are made continuously; altitude and heading drift unnoticed because the other instruments aren't being checked.

Why: the AI is the most intuitive instrument (it looks like a horizon) and the easiest to interpret. The brain naturally prefers it.

Fix: the AI is the anchor of the scan, not the destination. After every AI check, move to a primary instrument (altimeter, HI, or ASI), interpret it, then return to the AI. Cycle through all three primaries every 4–6 seconds.

2. Omitting an instrument from the scan

What it looks like: the pilot consistently checks altitude and heading but rarely looks at the airspeed. Airspeed drift accumulates unnoticed until it's a 15-kt bust.

Why: the omitted instrument feels "less important" or its drift is gradual.

Fix: the scan is a complete cycle. Every primary instrument is checked every cycle. The cycle is AI → primary → AI → primary → AI → primary → AI — three primaries, four AI checks, ~6 seconds.

3. Chasing the AI

What it looks like: the pilot adjusts pitch on every AI glance — small input, small input, small input. The airplane never settles.

Why: treating the AI as a control input target rather than a status indicator. Each "correction" is reacting to noise.

Fix: trim, then verify with the primary instrument. The AI gives instant feedback; the primary instrument is the truth. If altitude is on, pitch is on — regardless of what the AI shows momentarily. Don't chase the AI; verify against the primary.

4. Failing to trim after corrections

What it looks like: the pilot makes a pitch correction, holds it manually, then has to make the same correction again because the airplane returns to the original drift as soon as control pressure is released.

Why: trim is treated as an afterthought rather than as the foundation of relaxed control.

Fix: trim is the second step of every correction. Make the input → hold for stabilization → trim out the input → release. If you can't release, you didn't trim enough.

5. Large corrections

What it looks like: the altimeter shows the airplane is 200 ft low; the pilot pitches up aggressively to recover, overshooting the target altitude by 200 ft in the other direction.

Why: treating instrument flight like visual — large inputs feel "decisive."

Fix: small corrections, then verify. For a 100-ft altitude deviation, a 1–2° pitch change is plenty. Hold for 10 seconds; verify on the primary; adjust further if needed. The discipline scales with the deviation.

6. Trusting senses over instruments

What it looks like: the pilot feels the airplane is in a turn; the AI shows wings level. The pilot applies aileron to "correct" the perceived turn — banking the airplane out of a level attitude.

Why: vestibular sensation under sustained or coordinated flight conditions is unreliable (Task H K1 covers the physiology). The brain treats sensation as truth even when it's lying.

Fix: the instruments are correct; your senses are not. Apply the doctrine even when it feels wrong. Practice in slow flight (VII.A) and instrument straight-and-level (here) until trust becomes automatic. The cross-control discipline from IV.G applies: don't fight the airplane based on a sensation.

7. Breaking the scan during a correction

What it looks like: during an altitude correction, the pilot fixates on the altimeter to "watch the recovery." Meanwhile, heading drifts 15° because the HI hasn't been scanned in 20 seconds.

Why: the correction feels important enough to monopolize attention.

Fix: the scan continues during corrections. Watching the recovery is exactly what the cycle is for — return to the altimeter every 2 seconds, but in between, check the HI, the ASI, and the AI. The correction completes on its own if the trim is right.

How errors compound. Fixation (#1) leads to omission (#2) leads to scan breakdown (#7), which lets a drift accumulate before correction. Chasing (#3) without trim (#4) makes the corrections worse. The single discipline that prevents most errors: trim, then verify with the primary. A trimmed airplane in straight-and-level flight stays there until something changes; your job is to detect the change with the scan, not to constantly hold the airplane level by control input.