Preflight Procedures (Instrument Rating – Airplane, Area of Operation II)
Preflight Procedures (Area of Operation II)
This area of operation is judged in the airplane, before the wheels leave the ground: cockpit management, engine start, taxi, pre-takeoff checks, and the IFR-specific setup that decides whether your first two minutes in IMC are flyable.
Instrument system checks before takeoff
- Altimeter: set the current reported setting and compare with field elevation; tolerance is ±75 ft. If outside, do not depart IFR - resolve the static source or use a known-good source.
- Heading indicator: align to the magnetic compass before taxi, then recheck after turns; a few degrees of precession per hour is normal.
- Vacuum/pressure gauges: confirm suction in the green arc (typically 4.5–5.5 inHg) and that both attitude and heading gyros are erect.
- Pitot heat: check function during taxi when departing into visible moisture or known icing.
- Alternate static: know where the valve is; when selected, the airspeed indicator, altimeter, and VSI all read higher.
- Databases and charts current for the route, with both nav radios tuned for a quick cross-check.
Clearance and departure setup
Copy the clearance with CRAFT (Clearance limit, Route, Altitude, Frequency, Transponder), read it back in full, and set the assigned altitude in the alerter before taxi. Brief the departure: ODP or SID, initial heading, engine-out plan, and the action for lost communications. Under Part 91 there is no regulatory takeoff minimum, but a zero-zero departure from an airport with no return option is a decision you must be able to justify, and some ODPs publish ceiling and visibility requirements.
Worked example
The ATIS gives 29.92 and the field elevation is 700 ft. After setting it you read 780 ft - 80 ft of error, outside the 75-ft tolerance, so the altimeter is not legal for IFR. Re-set the altimeter to the known field elevation, record the 0.08 inHg correction, have the static system checked, and confirm with a second source before departure.
Traps that cost marks
Reading an 80-ft error as "close enough"; launching without cross-checking the heading indicator; skipping the lost-communications brief; taxiing heads-down while copying a clearance; and treating a clearance readback as optional.