Systems Preflight Procedures
Inspecting the instrument system requires a relatively small part of the total time required for preflight activities, but its importance cannot be overemphasized. Before any flight involving aircraft control by instrument reference, the pilot should check all instruments and their sources of power for proper operation.
NOTE: The following procedures are appropriate for conventional aircraft instrument systems. Aircraft equipped with electronic instrument systems utilize different procedures.
Before Engine Start
- Walk-around inspection: Check the condition of all antennas and check the pitot tube for the presence of any obstructions and remove the cover. Check the static ports to be sure they are free from dirt and obstructions, and ensure there is nothing on the structure near the ports that would disturb the air flowing over them.
- Aircraft records: Confirm that the altimeter and static system have been checked and found within approved limits within the past 24 calendar months. Check the replacement date for the emergency locator transmitter (ELT) batteries noted in the maintenance record, and be sure they have been replaced within this time interval.
- Preflight paperwork: Check the Airport/Facility Directory (A/FD) and all NOTAMs for the condition and frequencies of all the navigation aid (NAVAIDs) that are used on the flight. Handbooks, en route charts, approach charts, computer and flight log should be appropriate for the departure, en route, destination, and alternate airports.
- Radio equipment: Switches OFF.
- Suction gauge: Proper markings as applicable if electronic flight instrumentation is installed.
- ASI: Proper reading, as applicable. If electronic flight instrumentation is installed, check emergency instrument.
- Attitude indicator: Uncaged, if applicable. If electronic flight instrumentation is installed, check emergency system to include its battery as appropriate.
- Altimeter: Set the current altimeter setting and ensure that the pointers indicate the elevation of the airport.
- VSI: Zero indication, as applicable (if electronic flight instrumentation is installed).
- Heading indicator: Uncaged, if applicable.
- Turn coordinator: If applicable, miniature aircraft level, ball approximately centered (level terrain).
- Magnetic compass: Full of fluid and the correction card is in place and current.
- Clock: Set to the correct time and running.
- Engine instruments: Proper markings and readings, as applicable if electronic flight instrumentation is installed.
- Deicing and anti-icing equipment: Check availability and fluid quantity.
- Alternate static-source valve: Be sure it can be opened if needed, and that it is fully closed.
- Pitot tube heater: Check by watching the ammeter when it is turned on, or by using the method specified in the POH/AFM.
After Engine Start
- When the master switch is turned on, listen to the gyros as they spin up. Any hesitation or unusual noises should be investigated before flight.
- Suction gauge or electrical indicators: Check the source of power for the gyro instruments. The suction developed should be appropriate for the instruments in that particular aircraft. If the gyros are electrically driven, check the generators and inverters for proper operation.
- Magnetic compass: Check the card for freedom of movement and confirm the bowl is full of fluid. Determine compass accuracy by comparing the indicated heading against a known heading (runway heading) while the airplane is stopped or taxiing straight. Remote indicating compasses should also be checked against known headings. Note the compass card correction for the takeoff runway heading.
- Heading indicator: Allow 5 minutes after starting engines for the gyro to spin up. Before taxiing, or while taxiing straight, set the heading indicator to correspond with the magnetic compass heading. A slaved gyrocompass should be checked for slaving action and its indications compared with those of the magnetic compass. If an electronic flight instrument system is installed, consult the flight manual for proper procedures.
- Attitude indicator: Allow the same time as noted above for gyros to spin up. If the horizon bar erects to the horizontal position and remains at the correct position for the attitude of the airplane, or if it begins to vibrate after this attitude is reached and then slowly stops vibrating altogether, the instrument is operating properly. If an electronic flight instrument system is installed, consult the flight manual for proper procedures.
- Altimeter: With the altimeter set to the current reported altimeter setting, note any variation between the known field elevation and the altimeter indication. If the indication is not within 75 feet of field elevation, the accuracy of the altimeter is questionable and the problem should be referred to a repair station for evaluation and possible correction. Because the elevation of the ramp or hangar area might differ significantly from field elevation, recheck when in the run-up area if the error exceeds 75 feet. When no altimeter setting is available, set the altimeter to the published field elevation during the preflight instrument check.
- VSI: The instrument should read zero. If it does not, tap the panel gently. If an electronic flight instrument system is installed, consult the flight manual for proper procedures.
- Engine instruments: Check for proper readings.
- Radio equipment: Check for proper operation and set as desired.
- Deicing and anti-icing equipment: Check operation.
Taxiing and Takeoff
Ensuring the functionality of the turn coordinator, heading indicator, magnetic compass, and attitude indicator prior to taxiing and takeoff is essential to flight safety. Runway incursion is an incident at an airport that adversely affects runway safety and pilots must mitigate this risk by ensuring that all of the directional flight instruments are checked properly before taxiing or taking off so that the position of the aircraft in relation to the runway and other traffic is always known.
- Turn coordinator: During taxi turns, check the miniature aircraft for proper turn indications. The ball or slip/skid should move freely. The ball or slip/skid indicator should move opposite to the direction of turns. The turn instrument should indicate the direction of the turn. While taxiing straight, the miniature aircraft (as appropriate) should be level.
- Heading indicator: Before takeoff, recheck the heading indicator. If the magnetic compass and deviation card are accurate, the heading indicator should show the known taxiway or runway direction when the airplane is aligned with them (within 5°).
- Attitude indicator: If the horizon bar fails to remain in the horizontal position during straight taxiing, or tips in excess of 5° during taxi turns, the instrument is unreliable. Adjust the miniature aircraft with reference to the horizon bar for the particular airplane while on the ground. For some tricycle-gear airplanes, a slightly nose-low attitude on the ground gives a level flight attitude at normal cruising speed.
Engine Shut Down
When shutting down the engine, note any abnormal instrument indications.