ACS Task IR.II.C — Instrument Cockpit Check

What does ACS Task IR.II.C cover?

IR.II.C is the Instrument Cockpit Check task in the FAA Instrument Rating ACS (FAA-S-ACS-8C), filed under Area of Operation II — Technical Subject Areas. The task sits at the intersection of preflight planning and systems knowledge: the examiner expects you to demonstrate that you know why each check exists, which regulation requires it, and how to correctly identify and handle a discrepancy before you leave the ramp. This is not a walkaround — it is an avionics-and-flight-instruments verification performed from the cockpit, typically after engine start with systems powered.

What knowledge does the DPE test under IR.II.C?

The knowledge elements cover the regulatory basis for each check item and the practical limits a pilot uses to evaluate instrument health:

• Required IFR instruments and equipment under 14 CFR 91.205(d) (GRABCARD), and the inoperative-equipment deferral process under 14 CFR 91.213
• VOR operational check methods, tolerances, and logging requirements under 14 CFR 91.171
• Altimeter setting requirements under 14 CFR 91.121, and the 24-month certified altimeter/static system test under 14 CFR 91.411 and Part 43 Appendix E
• ATC transponder 24-month test requirement under 14 CFR 91.413 and transponder operational requirements under 14 CFR 91.215
• GPS navigation database currency standards and the distinction between WAAS receivers (real-time RAIM) and non-WAAS receivers (preflight RAIM prediction required)
• Vacuum and electrical power redundancy as it applies to instrument reliability in IMC
• Pitot heat system check and its relevance to airspeed indicator accuracy in icing or moisture conditions

What are the VOR check requirements under 14 CFR 91.171?

14 CFR 91.171(a) prohibits operating IFR using the VOR system unless the VOR has been operationally checked within the preceding 30 days and found within permissible bearing error. The cockpit check is where you confirm the logbook entry is current — not where you perform the check itself. The four acceptable methods and their tolerances are:

The cockpit check is also where you physically power up the VOR receiver and verify it is functional — tuning a nearby VOR station and confirming a valid flag-free course indication. If the check logbook entry is missing or expired, you may not legally use VOR for IFR navigation on that flight.

What does the altimeter check require?

Setting the current altimeter setting (obtained from ATIS, ASOS, or ATC) and comparing the altimeter reading to published field elevation is the standard preflight procedure. The FAA Instrument Flying Handbook (FAA-H-8083-15B) describes this comparison and treats a discrepancy of more than 75 feet as a practical indicator that the altimeter or static system warrants maintenance review before IFR flight — though the specific tolerance figure is guidance, not a hard regulatory limit imposed by the FARs on the pilot's preflight check.

The regulatory requirements are two separate items: under 14 CFR 91.205(d)(5) , the aircraft must have a sensitive altimeter adjustable for barometric pressure; and under 14 CFR 91.411 , the static pressure system and altimeter must have been tested and inspected within the preceding 24 calendar months and found to comply with 14 CFR Part 43 Appendix E by a certificated repair station. That certified test — not the pilot's preflight comparison — is where the specific scale-error tolerances (±20 ft near sea level, increasing with altitude) and the 75-foot hysteresis test limit apply.

What does the transponder check require?

During the cockpit check, confirm the transponder is operative, set to the correct code (typically 1200 for VFR or as assigned by ATC/clearance), and that the altitude encoding function (Mode C) is active. Under 14 CFR 91.215 , Mode C altitude reporting is required in Class A, B, and C airspace; within 30 nm of Class B airports (the Mode C veil); above Class B or C airspace within their lateral limits up to 10,000 feet MSL; and at and above 10,000 feet MSL nationwide (except at or below 2,500 feet AGL). Nearly every IFR departure falls within at least one of these areas, making the Mode C check operationally mandatory.

The maintenance currency check: under 14 CFR 91.413 , the transponder must have been tested within the preceding 24 calendar months and found to comply with 14 CFR Part 43 Appendix F. Verify the date in the aircraft maintenance records alongside the 91.411 altimeter check — both are 24-month items that expire together.

What does the GPS check require?

The GPS cockpit check has two independent elements: database currency and RAIM availability.

Database currency: The navigation database must be current (within its update cycle, typically 28 days for Jeppesen or AIRAC data) for IFR approach use. An expired database may be used for IFR en route navigation only if the pilot verifies that the procedures and waypoints have not changed and annotates the discrepancy in accordance with the GPS AFM supplement. For IFR approaches, the database must be current without exception.

RAIM check: For non-WAAS GPS receivers, the pilot must predict RAIM availability at the destination airport during the estimated time of arrival. RAIM prediction can be performed using the FAA's RAIM prediction tool at nasstatus.faa.gov or via the GPS receiver's built-in RAIM prediction function. WAAS receivers (e.g., a certified WAAS GPS approved per TSO-C146) provide real-time satellite integrity monitoring and do not require a preflight RAIM prediction check — the receiver will annunciate loss of integrity in flight if it occurs.

What other items does the cockpit check include?

1. 1
   Attitude indicator: confirm the gyro has erected fully and shows wings-level with aircraft aligned; flag is out of view
2. 2
   Heading indicator (directional gyro): align to magnetic compass with the aircraft stationary or taxiing straight; confirm precession is within normal limits
3. 3
   Turn coordinator or rate-of-turn indicator: verify power flag is absent; confirm ball is centered
4. 4
   Vertical speed indicator: confirm reading at zero (or within ±50 fpm of zero) with aircraft stationary
5. 5
   Airspeed indicator: confirm reading at zero on the ground
6. 6
   Magnetic compass: check for fluid leaks; confirm it reflects magnetic heading
7. 7
   Pitot heat: activate and verify element heats (use a careful touch on the probe exterior or confirm ammeter draw); deactivate before taxi on hot days
8. 8
   Vacuum system: confirm suction gauge reads within the green arc for gyroscopic instruments
9. 9
   Electrical system: verify alternator/generator output and bus voltage are within limits — electric backup instruments depend on this
10. 10
    Lighting: verify all cockpit and exterior lights are operative per 14 CFR 91.205(c) if night flight is planned

What risk management does the DPE expect?

The examiner evaluates whether you use the cockpit check as a genuine risk management tool — not a rote checklist recitation. The central risk under this task is departing with an undetected instrument discrepancy that will not become apparent until you are in IMC.

• Recognize that a subtle instrument anomaly on the ground (e.g., an attitude indicator that erects slowly, a heading indicator with excessive precession) can indicate a gyro problem that will worsen in flight
• Understand the consequence of an undetected Mode C failure: ATC cannot provide altitude separation, and the error may not be caught until a controller queries you
• Evaluate the impact of GPS database expiration on approach currency — an expired database discovered at the destination in IMC is a serious safety risk
• Know the 14 CFR 91.213 deferral process so you can make a sound go/no-go decision when a discrepancy is found, rather than guessing

What do DPEs look for during the cockpit check?

Examiners report that the most common weak points are: candidates who can cite the VOR tolerance but cannot locate or read the logbook entry in the actual aircraft; candidates who set the altimeter but do not compare it to field elevation; and candidates who cannot distinguish a WAAS receiver from a non-WAAS receiver when answering RAIM questions. Know the specific 24-month items (91.411 altimeter, 91.413 transponder) and be able to find the maintenance log dates in the aircraft documents — the DPE may hand you the logbooks and ask you to verify currency before the oral even begins.

• "Walk me through your instrument cockpit check for this aircraft."
• "The VOR check entry in the logbook is dated 32 days ago. What are your options?"
• "Your altimeter is set to 30.02 and reads field elevation as 850 feet. Published elevation here is 900 feet. Is that acceptable?"
• "This aircraft has a non-WAAS GPS. What is your RAIM check requirement before an IFR departure to an airport with a GPS approach?"
• "You find the altimeter/static system test was performed 25 months ago. Can you depart IFR?"
• "The attitude indicator is slow to erect. How does that affect your preflight decision?"

Common Errors

• Confusing the 24-month certified maintenance check (91.411 / 91.413) with the pilot-performed preflight comparison — the tests are performed by different people for different purposes
• Stating the VOR must be checked today, rather than within the preceding 30 days
• Confusing the ±75-foot IFH practical guideline with a hard regulatory tolerance from the FARs
• Skipping the GPS RAIM check on non-WAAS aircraft, or incorrectly requiring a RAIM prediction check for a WAAS-certified receiver
• Failing to verify 24-month maintenance currency dates in the aircraft logbooks — knowing the regulatory citation is not the same as confirming the aircraft is legal
• Omitting the pitot heat check, which protects the airspeed indicator in moisture and is particularly critical for flights into IMC

Practice Questions

1. You perform the altimeter cockpit check with the current altimeter setting dialed in. The altimeter reads 1,240 feet MSL; published field elevation is 1,100 feet. The 91.411 logbook entry shows testing 20 months ago. Identify every issue and the regulation that applies to each.

2. The VOR logbook entry shows a ground checkpoint check with a bearing error of 3.5°, signed and dated 29 days ago. Is the VOR check current for today's IFR departure? What is the applicable tolerance and regulatory citation?

3. Your aircraft has a non-WAAS GPS receiver. You plan an IFR flight that includes an RNAV (GPS) approach at the destination. What RAIM check is required, when must it be accomplished, and where can you obtain a RAIM prediction?

4. The aircraft transponder is inoperative on preflight. The aircraft has no FAA-approved MEL. You plan an IFR flight under ATC control through Class B airspace. Can you depart? Cite the specific regulations that govern your decision.

5. A DPE asks: "What is the difference between the 91.411 altimeter check and the altimeter check you perform during the cockpit check?" Explain both, who performs each, and what standard each applies.

Frequently Asked Questions

Q: What is ACS Task IR.II.C?

IR.II.C is the Instrument Cockpit Check task in the FAA Instrument Rating ACS (FAA-S-ACS-8C). It requires the applicant to verify that all required instruments and systems — including the VOR check, altimeter setting, transponder, pitot heat, and GPS database and RAIM — are operative and within limits before an IFR departure.

Q: What VOR check is required before IFR flight?

Under 14 CFR 91.171 , the VOR must have been operationally checked within the preceding 30 days and found within permissible bearing error: ±4° for a VOT or ground checkpoint, ±6° for an airborne checkpoint, and ±4° difference between dual independent VOR systems checked against the same station.

Q: What altimeter check does a pilot perform during the cockpit check?

The pilot sets the current altimeter setting and compares the reading to published field elevation. The Instrument Flying Handbook (FAA-H-8083-15B) cites ±75 feet as a practical guideline. The regulatory maintenance requirement is a certified 24-month static system and altimeter test under 14 CFR 91.411 and Part 43 Appendix E.

Q: What is the 24-month altimeter and transponder check requirement?

14 CFR 91.411 requires the static pressure system and altimeter to be tested within the preceding 24 calendar months and found to comply with 14 CFR Part 43 Appendix E. 14 CFR 91.413 separately requires the transponder to be tested within the preceding 24 calendar months, compliant with Part 43 Appendix F.

Q: What GPS database currency check is required before IFR flight?

The navigation database must be current for the departure date for IFR approach use. Per the GPS AFM supplement and FAA guidance, an expired database may not be used for IFR approaches. For en route IFR navigation, an expired database may be used only if the pilot verifies that procedures and waypoints are unchanged.

Q: What is a RAIM check and when is it required?

A RAIM check predicts GPS satellite availability at the destination during the expected arrival time. For non-WAAS GPS approaches, the pilot must confirm RAIM availability before departure using the FAA's RAIM prediction tool or the receiver's built-in prediction. WAAS GPS receivers provide real-time integrity monitoring and do not require a preflight RAIM prediction.

Q: Does the DPE actually watch you perform the cockpit check?

Yes. Under ACS Task IR.II.C Skill elements, the applicant must perform the cockpit check using the aircraft's POH/AFM procedures. The DPE evaluates that the check is systematic, that the applicant identifies any inoperative items, and that any discrepancy is correctly dispositioned under 14 CFR 91.213 .

Q: What instruments are required for IFR flight per 14 CFR 91.205?

14 CFR 91.205(d) requires GRABCARD for IFR: Generator/alternator, Radio (comm and nav suitable for the route), Attitude indicator, Ball (slip-skid indicator), Clock with seconds display, Altimeter adjustable for barometric pressure, Rate-of-turn indicator, and Directional gyro — plus all VFR day and night equipment from subsections (b) and (c).

Sources

• 14 CFR 91.171 — VOR Equipment Check for IFR Operations (Cornell LII)
• 14 CFR 91.205 — Instrument and Equipment Requirements (Cornell LII)
• 14 CFR 91.411 — Altimeter System and Altitude Reporting Equipment Tests (Cornell LII)
• 14 CFR 91.413 — ATC Transponder Tests and Inspections (Cornell LII)
• 14 CFR 91.215 — ATC Transponder and Altitude Reporting Equipment (Cornell LII)
• 14 CFR Part 43 Appendix E — Altimeter System Test Standards (Cornell LII)
• FAA Instrument Rating ACS (FAA-S-ACS-8C)
• FAA Instrument Flying Handbook (FAA-H-8083-15B)

This article was researched from FAA primary sources (14 CFR Part 91 via Cornell LII, Part 43 Appendix E, Instrument Rating ACS, Instrument Flying Handbook) and citing current regulatory text — drafted by MockDPE. Last updated: May 2026. If you spot an inaccuracy, email corrections@mockdpe.org.