FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsHard
An aircraft at 40°N latitude is turning from a heading of 270° (West) to a heading of 040°, passing through North. Using the standard lead rule for compass turns through north (lead equal to latitude), at approximately what indicated compass heading should the pilot begin rolling out to arrest the turn precisely on 040°?
- A000°
- B080°
- C350°
- D040°
Show answer & explanationAnswer & explanation
Correct answer: A. 000°
When turning through North, the compass lags, so the pilot must lead the rollout by an amount approximately equal to the latitude (40°). Subtracting 40° from the desired heading of 040° gives 000°, so the pilot should begin rollout when the indicated heading passes through North; the compass will then settle on 040° as the turn error dissipates.
Why the other options are wrong
- B. 080° would apply an excessive lead in the wrong direction for this turn.
- C. 350° reflects too little lead and would still result in an overshoot past 040°.
- D. Rolling out exactly at 040° ignores the lag error and would result in overshooting the desired heading.
Compass Lead for Turns Through North
When rolling out of a turn through North, pilots should lead the desired heading by an amount approximately equal to their latitude to compensate for compass lag.
- Lead amount ≈ latitude when turning through North
- No lead (or opposite) typically needed turning through South
- Applies mainly to standby/whiskey compass, not slaved HSI
Memory trick: Lead by your latitude when passing through North.