A PIREP (Pilot Report) is a real-time weather observation made by a pilot in flight and transmitted to air traffic control or a flight service station. It describes actual atmospheric conditions encountered at a specific location, altitude, and time.
How It Works#
Pilots file PIREPs verbally over the radio or through digital datalink systems. The report gets entered into the aviation weather system and broadcast to other pilots and dispatchers. A PIREP can be routine (UA) or urgent (UUA), with urgent reports reserved for severe conditions such as extreme turbulence or heavy icing.
Each PIREP follows a standard format with defined fields:
- OV (Location): position relative to a navaid or fix
- TM (Time): UTC time of observation
- FL (Flight Level): altitude in hundreds of feet
- TP (Aircraft Type): the reporting aircraft
- SK (Sky condition): cloud layers and coverage
- WX (Weather): precipitation or visibility restrictions
- TA (Air Temperature): outside air temp in Celsius
- WV (Wind): direction and speed
- TB (Turbulence): intensity and type
- IC (Icing): intensity and type
- RM (Remarks): any additional observations
Not every field is required in every report. Pilots include what they observe and omit fields that don't apply.
Example in Aviation#
A Cessna 172 pilot cruising at 8,500 feet near Denver reports moderate turbulence and light rime icing in cloud. The report reads:
UA /OV DEN /TM 1745 /FL085 /TP C172 /SK OVC /TA -4 /TB MOD /IC LGT RIME
A Boeing 737 crew planning the same route at FL180 receives that PIREP through their dispatcher or ATC. They know to expect icing conditions below their planned altitude and brief their approach accordingly.
Why It Matters#
Weather forecasts predict where hazards are likely to develop. PIREPs confirm where those hazards actually exist right now. A forecast may place turbulence at FL240, but a PIREP from 20 minutes ago shows it starting at FL210. That distinction can change a flight plan.
PIREPs are especially valuable in mountainous terrain and during convective activity, where conditions change faster than forecast models update. Filing a PIREP after encountering hazardous conditions is not just good practice — FAA regulations in 14 CFR §91.183 require pilots operating under IFR to report unforecast weather hazards to ATC.
Key Takeaways#
- A PIREP reports actual in-flight conditions, not forecast ones.
- Urgent PIREPs (UUA) cover severe turbulence, severe icing, and other immediate hazards.
- Standard format fields include location, altitude, aircraft type, and observed conditions.
- PIREPs fill gaps between forecast updates, especially in rapidly changing weather.
- IFR pilots are required by regulation to report unforecast hazardous conditions to ATC.