Instrument

# Timed Turns To Magnetic Compass Headings

Timed Turns To Magnetic Compass Headings

• Used to make turns in the event of a HI failure
• Two methods: Timed and compass

Timed Turns

• With rate held constant (3’per second)one can calculate the amount of time required to turn a specific number of degrees
• Determine the amount of bank: (KIAS/10) + 7 example: you are flying at 120 Kn e.g. 120/10=12 plus 7 = 19 19 degrees is your std bank for 120 kn.

Calibrating the turn coordinator:

• Must verify TC is truly calibrated at standard rate
• Aircraft should turn 45’ per quadrant of the clock(15seconds/3per second)
• If SHORT on MC increase TC one bar over std. rate trn.
• If LONG on MC decrease TC one bar under std. rate trn.

Performing a timed turn:

1. Determine the heading that must be flown
2. Determine your current heading with the magnetic compass (in level flight)
3. Determine the amount of time to reach the new HDG
4. Start time and immediately roll into a standard rate turn
5. *Monitor ALT & VSI
6. Roll out when the specified time has elapsed
7. Check heading on MC (mag compass)
8. If SHORT on MC increase TC one bar over std. rate trn.
9. If LONG on MC decrease TC one bar under std. rate trn.

Compass Turns

• Compass is the only direction-indicating instrument independent of the aircraft
• Normally used to set and check the HI but with compensation for errors it can be used to make turns
• Abrupt movements and accelerations have a big effect
• Compass appears to move in opposite direction of turn
• Errors:
1. If you are on a N heading and you start a turn to the E or W, the compass indication lags, or shows a turn in the opposite direction.
2. If you are on a S heading and you start a turn toward the E or W, the compass indication speeds up ahead of the turn, showing a greater amount of turn than is actually occurring.
3. When you are on an E or W heading, the compass indicates correctly as you start a turn in either direction.
4. If you are on an easterly or westerly heading, acceleration results in a northerly turn indication; deceleration results in a southerly turn indication.
5. If you maintain a north or south heading, no error results from diving, climbing, or changing airspeed.
• ANDS(anticipate and accelerate north) UNOS
• Lead and lag is determined by the latitude at which you are flying
• N – 26’+ ½ bank angle (7’) = 33’
• S – 26’-7’=19’