FAR Explainer · 91.187
14 CFR 91.187 — IFR Malfunction Reports (Explained)
What you must report to ATC when nav or comm equipment malfunctions in controlled airspace under 14 CFR 91.187 — the (b) four-item content of the report.
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14 CFR 91.187 — IFR Malfunction Reports (Explained)
When does 14 CFR 91.187 apply?
14 CFR 91.187(a) requires the PIC to report "as soon as practical to ATC any malfunctions of navigational, approach, or communication equipment occurring in flight." Three conditions activate the duty to report: the flight is operating under IFR, the failure involves navigational, approach, or communication equipment, and the flight is operating in controlled airspace where ATC separation services apply.
The regulation covers any qualifying malfunction — total failure, partial failure, and degraded performance all count if they affect IFR capability. "As soon as practical" reflects the aviate-navigate-communicate priority: stabilize the aircraft first, then report. ATC does not expect an immediate call if the crew is managing an emergency workload.
What four items must the report include under 91.187(b)?
14 CFR 91.187(b) specifies exactly four items every malfunction report must contain. The regulation uses the word "must," making each item mandatory, not discretionary.
- 1Aircraft identification — your callsign or registration, so ATC can associate the report with your flight strip.
- 2Equipment affected — the specific system or component that has malfunctioned (e.g., 'VOR receiver number one,' 'transponder Mode C,' 'GPS navigator').
- 3Degree to which the capability of the pilot to operate under IFR in the ATC system is impaired — partial or total; whether you can continue the flight IFR or require routing changes.
- 4Nature and extent of assistance desired from ATC — vectors, radar monitoring, priority handling, coordination with destination, or no assistance required.
Item 3 is the most nuanced. "Degree" implies a spectrum: a failed GPS on an aircraft with functional VORs is a lesser impairment than a failed VOR on a GPS-only aircraft flying a VOR-based clearance. Quantify what you can still do versus what you cannot.
Item 4 drives ATC's response. Controllers cannot read your mind — if you want radar vectors to final to avoid depending on a failed nav aid, say so explicitly. If you need no assistance and simply want the malfunction on record, state that.
How does 91.187 relate to 91.183 and 91.185?
These three regulations form the core IFR communication framework, but each covers a distinct situation.
| Regulation | Trigger | What You Report |
|---|---|---|
| 14 CFR 91.183 | Routine IFR flight in controlled airspace | Position reports, unexpected weather, safety information |
| 14 CFR 91.187 | Equipment malfunction during IFR flight | Aircraft ID, equipment affected, IFR impairment, assistance desired |
| 14 CFR 91.185 | Total two-way radio communications failure | No report possible — follow the prescribed route/altitude/timing procedure |
14 CFR 91.183 requires position reports at designated reporting points, reports of unexpected weather, and any other safety-of-flight information. A transponder failure goes to 91.187; an unexpected encounter with icing goes to 91.183(b). The two regulations can trigger simultaneously if, for example, unexpected severe turbulence also damages a nav receiver.
14 CFR 91.185 applies when two-way communication is lost entirely — the scenario where 91.187 reporting is no longer possible. In that case the pilot follows the prescribed route (last assigned, expected, or filed), altitude (highest of last assigned, MEA, or expected), and timing procedures to execute the approach without ATC contact.
Worked examples of 14 CFR 91.187 reports
GPS RAIM unavailable
You are flying a GPS-based IFR clearance and your navigator displays a RAIM alert indicating it cannot guarantee position accuracy for the current phase of flight. This is a navigational equipment malfunction that impairs IFR capability.
A compliant 91.187(b) report:
"Center, Cessna 7842L, GPS RAIM unavailable, unable to navigate GPS as cleared. Requesting vectors to the VOR approach or a revised clearance via [VOR airway]."
That single transmission covers all four items: callsign, GPS navigator affected, unable to navigate GPS IFR (degree of impairment), and vectors or reroute requested (assistance desired).
Transponder Mode C failure
Your altitude encoder fails in flight. Your transponder squawks your code but ATC loses altitude readout. The malfunction affects approach and IFR capability because many terminal areas require Mode C by regulation.
A compliant 91.187(b) report:
"Approach, Piper 4386R, transponder altitude encoder inoperative. ATC has no Mode C readout. Requesting continued IFR clearance — advise if coordination required for Class B airspace ahead."
Altimeter failure
One of your two altimeters becomes unreliable at cruise. With a single altimeter you can continue IFR but with reduced redundancy; the degree of impairment is partial.
A compliant 91.187(b) report:
"Center, Baron 8812T, left altimeter failed, right altimeter operational. IFR capability partially impaired — single altimeter remaining. No additional assistance required at this time, monitoring closely."
What does a DPE ask about 14 CFR 91.187 on the oral exam?
Examiners approach 91.187 in two phases: citation and application. First, they confirm you know the regulation exists and can name the four required report elements. Then they present a failure scenario and ask you to construct the call.
- Citation — 'What FAR requires you to report a navigation equipment failure to ATC?' (Answer: 14 CFR 91.187.)
- Four-item recitation — 'What must that report include?' (Aircraft ID, equipment affected, degree of IFR impairment, assistance desired.)
- Scenario — 'Your GPS fails 30 miles from the destination on an IFR clearance. Walk me through your report.' (Apply all four items to the specific scenario.)
- Distinction — 'What is the difference between what you report under 91.183 and 91.187?' (Routine reports vs. equipment malfunction reports.)
- Edge case — 'If your radio fails completely, what regulation applies and how does it differ?' (91.185 — follow prescribed route/altitude/timing procedures instead of reporting.)
Practice Questions
- 1
Under 14 CFR 91.187(a), when must the PIC report an equipment malfunction to ATC?
Examiner GuidanceAs soon as practical after the malfunction occurs. The regulation applies to malfunctions of navigational, approach, or communication equipment during IFR flight. - 2
List the four items required in a 14 CFR 91.187(b) malfunction report.
Examiner GuidanceAircraft identification; equipment affected; the degree to which the capability of the pilot to operate under IFR in the ATC system is impaired; and the nature and extent of assistance desired from ATC. - 3
Your VOR receiver fails during an IFR flight. You have a functional GPS and can continue on the GPS-based clearance. Construct a 91.187(b)-compliant radio call.
Examiner GuidanceAn example: 'Center, Cessna 1234X, VOR receiver inoperative. GPS operational, able to continue IFR via GPS clearance. No additional assistance required.' This covers all four items: ID, equipment, degree of impairment (partial — GPS available), and assistance desired (none). - 4
Your transponder fails completely on an IFR flight. What regulation requires you to report it, and what four items must you include?
Examiner Guidance14 CFR 91.187 requires the report. The four items are: aircraft identification, transponder as the equipment affected, the degree of IFR impairment (ATC loses radar identification and altitude data), and the assistance desired (e.g., position reports in lieu of transponder, or request for handling). - 5
How does 14 CFR 91.187 differ from 14 CFR 91.185 in the context of a radio failure?
Examiner GuidanceIf only nav or approach equipment fails but communication is intact, 91.187 applies and you report the malfunction to ATC. If two-way radio communication fails entirely, 91.185 applies — reporting is impossible, and the pilot follows the prescribed route, altitude, and timing procedures to execute an approach without contact.
Frequently Asked Questions
Q: When must you report an equipment malfunction under 14 CFR 91.187?
Under 14 CFR 91.187(a), the PIC must report as soon as practical to ATC any malfunction of navigational, approach, or communication equipment that occurs in flight. The regulation applies in controlled airspace while operating under IFR.
Q: What four items must a 14 CFR 91.187 malfunction report include?
Under 14 CFR 91.187(b), the report must include: (1) aircraft identification, (2) equipment affected, (3) the degree to which IFR capability in the ATC system is impaired, and (4) the nature and extent of assistance desired from ATC.
Q: Does 91.187 apply to VFR flights?
No. 14 CFR 91.187 applies only to aircraft operated under IFR. The regulation's language references impairment of the capability to operate under IFR in the ATC system, which has no equivalent obligation for VFR operations.
Q: Do you need to report a GPS RAIM alert under 91.187?
Yes, if RAIM loss prevents navigation via GPS while IFR. The malfunction affects navigational equipment and impairs IFR capability per 14 CFR 91.187(a). Include the assistance desired — vectors, reroute, or a different approach procedure.
Q: What is the difference between 91.183 and 91.187?
14 CFR 91.183 covers routine IFR communications: position reports, unexpected weather, and safety information. 14 CFR 91.187 is specific to equipment malfunctions. A transponder failure triggers 91.187; an unexpected icing encounter triggers 91.183(b).
Q: If your transponder Mode C fails in flight, what do you report?
Report under 14 CFR 91.187(b): aircraft identification, that the transponder Mode C altitude encoder is affected, the degree of impairment (ATC loses altitude readout), and the assistance desired — typically continued IFR clearance and coordination for any Class B or Mode C required airspace ahead.
Q: Does a partial nav failure require a 91.187 report?
Yes. 14 CFR 91.187(b)(3) requires reporting the degree to which capability is impaired — the word "degree" indicates that partial impairment triggers the reporting duty. A failed VOR receiver on a single-VOR aircraft operating a VOR clearance is a reportable malfunction even if GPS backup exists.
Q: What does "as soon as practical" mean in 91.187(a)?
It means report as quickly as workload and safety of flight permit. 14 CFR 91.187(a) does not require an instantaneous call. Aviate and navigate first; communicate the malfunction once the aircraft is stable and workload allows.
Sources
- 14 CFR 91.187 — IFR Malfunction Reports (Cornell LII)
- 14 CFR 91.185 — IFR Operations: Two-way Radio Communications Failure (Cornell LII)
- 14 CFR 91.183 — IFR Communications (Cornell LII)
- FAA Instrument Flying Handbook (FAA-H-8083-15B)
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This article was researched from FAA primary sources (14 CFR Part 91 via Cornell LII, Instrument Flying Handbook FAA-H-8083-15B) and citing current regulatory text — drafted by MockDPE. Last updated: May 2026. If you spot an inaccuracy, email corrections@mockdpe.org.
Frequently Asked Questions
When must you report an equipment malfunction under 14 CFR 91.187?
Under 14 CFR 91.187(a), the PIC must report as soon as practical to ATC any malfunction of navigational, approach, or communication equipment that occurs in flight. The regulation applies in controlled airspace while operating under IFR.
What four items must a 14 CFR 91.187 malfunction report include?
Under 14 CFR 91.187(b), the report must include: (1) aircraft identification, (2) equipment affected, (3) the degree to which IFR capability in the ATC system is impaired, and (4) the nature and extent of assistance desired from ATC.
Does 91.187 apply to VFR flights?
No. 14 CFR 91.187 applies only to aircraft operated under IFR. The regulation's language references impairment of 'the capability of the pilot to operate under IFR in the ATC system,' which has no equivalent obligation for VFR flights.
Do you need to report a GPS RAIM alert under 91.187?
Yes, if RAIM loss prevents you from navigating via GPS while IFR. The malfunction affects navigational equipment and impairs IFR capability, which triggers the reporting duty under 91.187(a). You should also request rerouting or vectors as desired per 91.187(b)(4).
What is the difference between 91.183 and 91.187?
14 CFR 91.183 covers routine IFR communications — position reports, weather, and safety information. 14 CFR 91.187 is specific to equipment malfunctions. A transponder failure triggers 91.187; an unexpected icing encounter you report under 91.183(b).
If your transponder Mode C fails in flight, what do you report?
Report under 14 CFR 91.187(b): your aircraft identification, that the transponder Mode C altitude encoder is affected, the degree of impairment (ATC loses altitude data), and the assistance desired — typically continued IFR clearance and coordination for airspace where Mode C is required.
Does a partial nav failure require a 91.187 report?
Yes, if it impairs IFR capability to any degree. 91.187(b)(3) requires reporting 'the degree to which' capability is impaired — the word 'degree' implies partial impairment counts. A VOR receiver out on a dual-VOR aircraft where the other is functional still warrants a report.
What does 'as soon as practical' mean in 91.187(a)?
It means report as quickly as the workload and safety of flight permit — aviate, navigate, and communicate in that priority order. ATC understands a pilot experiencing an equipment failure may need a moment to stabilize the aircraft before transmitting.
AI-generated study aid — not an official source. This article was written entirely by AI working from FAA primary sources (Instrument Rating ACS, 14 CFR Part 91, Aeronautical Information Manual, Instrument Flying Handbook, and relevant Advisory Circulars), with sources cited inline so you can verify each claim. It has not been reviewed by a CFI, DPE, or other certificated aviation professional. AI can hallucinate, misstate section numbers, and subtly paraphrase regulations in ways that change their meaning. Treat this page as a study starting point only — always confirm any regulatory, procedural, or operational fact against the linked FAA primary document before relying on it for a checkride, a written exam, or a flight. Last updated May 17, 2026. Spotted an error? Email corrections@mockdpe.org.