What is a PIREP and why is it important for IFR flight?

A PIREP (Pilot Weather Report) is a real-time weather observation made by a pilot in flight and relayed to air traffic control or a flight service station for distribution to other aviators. PIREPs are critical for IFR safety because official forecasts and ground-based observations cannot always capture actual in-flight conditions such as turbulence, icing, or cloud layers. The FAA's Aviation Weather Handbook emphasizes that PIREPs fill gaps between official products, making them among the most timely and operationally relevant weather sources available to instrument pilots.

How do you read a PIREP report, and what do the coded fields mean?

A PIREP is formatted in a standardized structure that begins with the reporting station identifier, followed by fields for location (/OV), time (/TM), altitude (/FL), aircraft type (/TP), sky conditions (/SK), flight visibility (/FV), weather (/WX), temperature (/TA), wind (/WV), turbulence (/TB), icing (/IC), and remarks (/RM). For example, a turbulence entry of MOD indicates moderate turbulence, while icing entries use standardized intensity terms such as LGT, MOD, or SEV. The FAA Instrument Flying Handbook and Aviation Weather Handbook both provide decoding guidance, and student pilots studying for the FAA Instrument Rating Airplane Airman Certification Standards should practice reading PIREPs using these references.

What's the difference between a routine PIREP (UA) and an urgent PIREP (UUA)?

A routine PIREP is coded UA and reports general flight conditions such as cloud tops, flight visibility, or light turbulence that are useful but not immediately hazardous. An urgent PIREP is coded UUA and is reserved for conditions that pose an immediate hazard to flight operations, including severe or extreme turbulence, severe icing, or low-level wind shear. Per the AIM, controllers are required to solicit PIREPs when hazardous conditions are reported or suspected, and urgent PIREPs receive priority handling and rapid dissemination to alert other pilots as quickly as possible.

Pilot Weather Reports (PIREPs): Reading and Filing

No weather product is more honest than a Pilot Weather Report (PIREP). While forecasts are produced by meteorologists working from numerical models and surface observations, only a pilot actually flying through the air can report what conditions truly exist at altitude. PIREPs — pronounced "pie-reps" — capture that real-world data and feed it back into the weather system so every pilot who comes after benefits. For instrument-rated pilots operating in the IFR environment, PIREPs are both an essential preflight planning tool and a professional obligation. Understanding how to read them fluently and how to file them accurately is a core instrument-rating skill.

The FAA's Aviation Weather Handbook (FAA-H-8083-28) identifies PIREPs as one of the primary sources of in-flight weather information. They are collected by Flight Service Stations (FSS), approach control facilities, and Air Route Traffic Control Centers (ARTCCs) and then distributed through standard weather dissemination channels including Aviation Weather Center products, ATIS broadcasts, and pilot weather briefings. Because they reflect actual observed conditions — not modeled predictions — they carry special weight when forecasts and reality diverge.

PIREP Structure: Decoding the Format

Every PIREP follows a standardized format defined by the FAA and encoded using specific two- or three-letter identifiers called descriptors. Learning these identifiers lets you read any PIREP at a glance. PIREPs come in two types: UA (routine PIREP) and UUA (urgent PIREP). A UUA is filed when the pilot encounters hazardous conditions such as severe turbulence, severe icing, or low-level wind shear, and it receives priority dissemination.

The fields in a standard PIREP appear in a fixed sequence:

/OV (Location): The position of the observation, given as a navaid identifier or an offset from a navaid (e.g., /OV ABC045025 means 25 nautical miles on the 045-degree radial from the ABC VOR).
/TM (Time): The time of the observation in UTC (Zulu), expressed as a four-digit group (e.g., /TM 1435).
/FL (Altitude/Flight Level): The altitude in hundreds of feet MSL, or UNKN if altitude is not known. For example, /FL085 means 8,500 feet MSL.
/TP (Aircraft Type): The aircraft type using standard abbreviations (e.g., /TP C172, /TP BE36). This matters because different aircraft have different performance characteristics, and a report of "light turbulence" in a heavy airliner might be moderate turbulence in a light single.
/SK (Sky Condition): Cloud layers, tops, and bases expressed in hundreds of feet MSL, along with coverage descriptors (FEW, SCT, BKN, OVC) and cloud type if relevant (e.g., /SK OVC065 means an overcast layer with bases at 6,500 feet MSL; /SK BKN030-TOP085 means a broken layer from 3,000 to 8,500 feet).
/WX (Flight Visibility and Weather): Reported in standard weather abbreviations (e.g., /WX FV03SM HZ means three-statute-mile visibility in haze).
/TA (Temperature): Outside air temperature in degrees Celsius at the reported altitude (e.g., /TA -12).
/WV (Wind): Direction in degrees true and speed in knots (e.g., /WV 27045KT means wind from 270° at 45 knots).
/TB (Turbulence): Reported using standardized intensity and type descriptors — NEG (none), LGT (light), MOD (moderate), SEV (severe), or EXTRM (extreme), along with whether it was continuous (CONT) or intermittent (INTMT) and the altitude range.
/IC (Icing): Icing intensity (NEG, TRC, LGT, MOD, SEV) combined with icing type (RIME, CLR, or MXD for mixed), and the altitude range (e.g., /IC MOD RIME 060-090).
/RM (Remarks): Any additional free-text comments the pilot wants to add — often the most valuable part of the report.

Turbulence and Icing Intensity: The Standard Scale

The standardized intensity scales for turbulence and icing are among the most commonly tested elements of PIREPs, and getting them right matters operationally. For turbulence, the Aviation Weather Handbook defines intensities based on their effect on the aircraft and occupants:

Light: Slight, erratic changes in altitude or attitude. Occupants may feel slight strain against seat belts. Loose objects may move slightly.
Moderate: Similar to light but of greater intensity. Airspeed variations may occur. Occupants feel definite strain against seat belts.
Severe: Large, abrupt changes in altitude or attitude. Aircraft may be momentarily out of control. Occupants are forced violently against seat belts.
Extreme: The aircraft is violently tossed about and practically impossible to control. May cause structural damage.

For icing, the type matters as much as the intensity. Rime ice forms when supercooled small droplets freeze rapidly on contact, producing a rough, opaque, milky deposit — common in stratiform clouds. Clear (glaze) ice forms when larger supercooled droplets spread before freezing, creating a dense, transparent, very aerodynamically disruptive coating — common in cumuliform clouds and at temperatures near 0°C. Mixed ice is a combination of both. Intensity runs from Trace (barely perceptible accumulation) through Light, Moderate, and Severe (rate of accumulation so great that de-icing equipment fails to reduce or control the hazard).

How to File a PIREP

Filing a PIREP is straightforward and can be done at any time during flight. Pilots should contact the nearest FSS, approach control, or ARTCC and state that they have a PIREP to file. ATC or FSS will record the information using the standardized format described above. PIREPs can also be filed electronically via certain EFB applications and forwarded to the FAA system, though voice filing over radio remains the most immediate method, especially for urgent reports.

When preparing to file, mentally organize your report before keying the mic: your location relative to a nearby navaid, your altitude, your aircraft type, and then the specific conditions — sky, visibility, temperature, winds, turbulence, icing — in that order. You do not need to include fields for which you have nothing to report; simply omit them. However, negative reports are valuable. A PIREP that says "NEG ICG NEG TURB" at a given altitude tells the next pilot that conditions are clean there, which is just as operationally useful as a hazard report.

Why PIREPs Matter for IFR Flight

In the IFR environment, cloud tops, icing layers, and turbulence bands can shift significantly from what Terminal Aerodrome Forecasts (TAFs) or Airmet/Sigmet products describe. PIREPs provide ground truth that no model can replicate. An Airmet Sierra covering a broad region for mountain obscuration tells you clouds exist; a PIREP saying "OVC bases 080, tops 120, smooth" tells you exactly where to fly to be on top in smooth air — a very different kind of information.

For icing specifically, PIREPs are often the only real-time evidence of where structural icing is occurring. The FAA's icing SIGMETs and Airmets are broad-area alerts, but pilots in the field who report icing at a specific altitude and location give ATC and other pilots the resolution to route around hazards. In areas without radar coverage, this can be life-saving information.

Regulation also touches PIREPs indirectly: under 14 CFR Part 91, pilots are expected to operate safely within the limits of their aircraft's certification and their own certificate. Flying into known icing conditions in an aircraft not certified for flight in known icing (FIKI) is prohibited. Current PIREPs are a primary tool for identifying — and avoiding — those conditions.

Key Numbers and Rules

A UUA (Urgent PIREP) must be filed for severe or extreme turbulence, severe icing, or low-level wind shear — these receive immediate priority dissemination.
Icing intensity of Severe means de-icing equipment cannot keep up with accumulation — immediate exit from the icing environment is required.
PIREP locations are given in nautical miles and degrees true from a navaid (not magnetic).
Temperatures in PIREPs are always in degrees Celsius.
Winds in PIREPs are in degrees true and knots, consistent with upper-level winds aloft conventions.
PIREPs are valid only for the conditions at the time and location reported — they are point-in-time observations, not forecasts.
Sky condition altitudes in PIREPs are reported in MSL, unlike surface METAR cloud heights which are AGL. This distinction is critical when comparing products.

Common Test Traps

MSL vs. AGL confusion: PIREP cloud heights are MSL, but METAR cloud heights are AGL. When comparing a PIREP reporting a 6,000-foot overcast to a METAR, you must account for field elevation to find the true ceiling above the ground.
True vs. magnetic wind direction: PIREPs and Winds Aloft Forecasts report wind direction in degrees true. Surface observations (METARs, ATISs) report magnetic. Mixing these up on a test — or in the cockpit — produces significant navigation errors.
Aircraft type significance: The FAA test may ask why aircraft type is included in a PIREP. The correct answer is that turbulence intensity is relative to aircraft size and mass; light turbulence in a Boeing 737 could be moderate or severe in a Cessna 172.
Negative PIREPs have value: Many students assume only hazard reports matter. A clean-air PIREP (NEG TB, NEG IC) is operationally significant and should be filed and used in planning.
UUA versus UA: Failing to recognize that a UUA triggers immediate dissemination — or not knowing what conditions mandate a UUA — is a common knowledge-test error. Severe turbulence, severe icing, and LLWS all qualify.