What is the difference between a UA and a UUA PIREP?

UA designates a routine pilot weather report, while UUA designates an urgent PIREP. A UUA is issued when the pilot reports severe or extreme turbulence, severe icing, or another immediately hazardous condition such as active volcanic ash. Urgent PIREPs receive priority handling by ATC and flight service to ensure rapid dissemination.

How are turbulence intensity levels defined in a PIREP?

PIREPs use four turbulence intensities: light (slight erratic changes, mild seat-belt strain), moderate (definite strain, aircraft remains in control, objects dislodged), severe (abrupt changes, possible momentary loss of control, occupant injury possible), and extreme (practically impossible to control, potential structural damage). Frequency descriptors — occasional, intermittent, and continuous — are added to indicate how much of the flight time the turbulence occupied.

What icing types are reported in PIREPs and which is most dangerous?

Pilots report icing as rime, clear (glaze), or mixed. Clear ice is generally considered the most aerodynamically dangerous because large supercooled droplets run back before freezing, forming a dense, smooth layer that closely conforms to the airfoil and is difficult to shed. Rime ice freezes instantly on contact, creating a more brittle, opaque accumulation. Mixed ice combines both characteristics and can be equally hazardous due to its irregular shape and density.

PIREP Encoding and Turbulence/Icing Intensity Reporting

Pilot Weather Reports, universally known as PIREPs, are among the most operationally valuable weather products available to aviators. Unlike model forecasts or radar composites, a PIREP represents a direct, real-time observation of atmospheric conditions at a specific altitude and location — information no ground-based sensor can fully replicate. For airline transport pilot candidates and working professionals alike, the ability to correctly encode, decode, and apply PIREPs is both a knowledge-test requirement and a genuine safety skill.

PIREPs are collected by air traffic controllers, flight service specialists, and in some cases automated datalink systems. They are then disseminated through standard weather products and, on many routes, shared via ATIS broadcasts and SIGMET advisories. The FAA Aviation Weather Handbook (FAA-H-8083-28B) is the primary source governing how PIREPs are formatted and how their intensity descriptors are defined.

PIREP Format and Encoding Structure

Every routine PIREP (UA) or urgent PIREP (UUA) follows a rigid, slash-delimited format composed of a defined set of elements. Urgent PIREPs are issued when a pilot reports severe or extreme turbulence, severe icing, or other conditions of immediate concern to flight safety; these are given priority handling by ATC and flight service. Understanding each element prevents misreading or omitting critical data.

UA or UUA — Report type: routine (UA) or urgent (UUA).
/OV — Location: given as a VOR identifier, fix, or fix bearing/distance (e.g., OV ABQ045025 means 025° at 25 nm from ABQ).
/TM — Time in UTC (Zulu), four digits (e.g., TM 1435).
/FL — Altitude or flight level in hundreds of feet MSL (e.g., FL085 = 8,500 ft MSL). UNKN is used when altitude is uncertain.
/TP — Aircraft type (e.g., TP B738). This is critical because an identical turbulence encounter feels very different to a Cessna 172 versus a Boeing 737.
/SK — Sky condition: cloud bases, tops, and coverage using standard contractions.
/WX — Flight visibility and present weather using standard weather contractions.
/TA — Air temperature in degrees Celsius (e.g., TA M20 = -20°C). Negative values are preceded by M.
/WV — Wind direction and speed in degrees and knots (e.g., WV 27045KT).
/TB — Turbulence intensity, frequency, and altitude range if different from /FL.
/IC — Icing type and intensity, and altitude range.
/RM — Remarks: free-text additional information such as LLWS (low-level wind shear), mountain wave activity, or volcanic ash.

Not every element is required for every PIREP. However, location (/OV), time (/TM), altitude (/FL), and aircraft type (/TP) are always mandatory. Omitting aircraft type degrades the report's value considerably, since a light aircraft and a heavy jet experience the same air mass very differently.

Turbulence Intensity Reporting

The turbulence intensity scale used in PIREPs has four levels, each defined by the effect on the aircraft and occupants. These definitions are standardized in FAA-H-8083-28B and must be memorized precisely, because the differences between categories carry major operational and regulatory implications.

Light turbulence: Slight, erratic changes in altitude and/or attitude. Occupants may feel slight strain against seat belts. Unsecured objects may be displaced slightly. Food and drink service may still be possible.
Moderate turbulence: Similar to light but of greater intensity. Changes in altitude and/or attitude occur, but the aircraft remains in positive control at all times. Occupants feel definite strain against seat belts. Unsecured objects are dislodged. Food and drink service is difficult or impossible.
Severe turbulence: Abrupt changes in altitude and/or attitude. Aircraft may be momentarily out of control. Occupants are forced violently against seat belts. Unsecured objects are hurled about. Food and drink service is impossible and injury to occupants is possible.
Extreme turbulence: The aircraft is violently tossed about and is practically impossible to control. It may cause structural damage. This is an extremely rare category, associated with severe thunderstorms or exceptionally intense mountain wave rotors.

In addition to intensity, pilots report turbulence frequency using three descriptors: Occasional (less than 1/3 of the time), Intermittent (1/3 to 2/3 of the time), and Continuous (more than 2/3 of the time). These frequency descriptors are appended to the intensity (e.g., MOD OCNL, SEV CONT). The altitude range over which turbulence was experienced is also reported when it spans a layer (e.g., TB MOD 080-110).

A special notation, CHOP, is sometimes appended to describe turbulence that produces rapid, rhythmic bumpiness without appreciable changes in altitude — commonly associated with jet stream edges or CAT (clear-air turbulence). LLWS in the remarks section flags low-level wind shear, a separate and critical hazard in the terminal environment.

Icing Intensity Reporting

Structural icing observed in flight is reported in the /IC element using both an intensity descriptor and a type descriptor. The intensity scale, like turbulence, runs from trace through severe.

Trace icing: Ice becomes perceptible. The rate of accumulation is slightly greater than the rate of sublimation. Deicing or anti-icing equipment is not normally required unless encountered for an extended period, more than one hour.
Light icing: The rate of accumulation may create a problem if flight continues for more than one hour. Occasional use of deicing or anti-icing equipment removes or prevents accumulation.
Moderate icing: The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing or anti-icing equipment or a diversion is necessary.
Severe icing: The rate of accumulation is such that deicing or anti-icing equipment fails to reduce or control the hazard. An immediate diversion is necessary.

Icing type is reported alongside intensity using standard contractions: RIME (rime ice, formed from supercooled water droplets freezing on contact, typically in stratiform clouds), CLEAR (clear or glaze ice, formed from larger droplets that partially freeze, producing a smooth, dense, and aerodynamically dangerous accretion), and MIXED (a combination of both, often the most hazardous because it combines density with irregular shape). A sample /IC element might read: IC MOD CLEAR 080-100, indicating moderate clear icing between 8,000 and 10,000 feet MSL.

Why PIREPs Matter Operationally

PIREPs are a cornerstone of the collaborative aviation weather system precisely because they fill gaps that no other product can. SIGMETs and AIRMETs for turbulence and icing are forecasts — educated predictions with inherent uncertainty. A PIREP is an observation. When a PIREP confirms that moderate icing exists at a forecast level, confidence in the SIGMET rises dramatically. When multiple PIREPs show smooth air through a turbulence AIRMET area, a dispatcher and flight crew have real data to support a route decision.

For Part 121 operations, PIREPs factor directly into flight release decisions and in-flight diversions. Under 14 CFR Part 91 and the AIM, pilots are encouraged — and in some circumstances expected — to file PIREPs whenever they encounter or fail to encounter forecast conditions. The AIM specifically requests PIREPs when encountering icing, turbulence of moderate or greater intensity, volcanic ash, or low-level wind shear. Filing timely PIREPs is a professional obligation, not just a courtesy.

Key Numbers and Rules

Turbulence frequency thresholds: Occasional <1/3, Intermittent 1/3–2/3, Continuous >2/3 of the time.
Trace icing becomes a concern after more than one hour of exposure without deicing equipment.
Light icing may become hazardous after more than one hour of continuous encounter.
Moderate icing: even short encounters are potentially hazardous — equipment use or diversion required.
Severe icing: equipment is ineffective — immediate diversion required.
Severe or extreme turbulence reports automatically trigger an urgent PIREP (UUA).
Temperature in PIREPs is always in degrees Celsius; negative values prefixed with M.
Location offsets use bearing (magnetic) and distance in nautical miles from a named fix.

Common Test Traps

Confusing icing intensity with icing type: Rime, clear, and mixed are types; trace, light, moderate, and severe are intensities. The exam often tests whether candidates know that clear ice is aerodynamically worse than rime, even at the same reported intensity.
Missing the UUA trigger: Only severe and extreme turbulence, severe icing, and certain other critical conditions (e.g., active volcanic ash) elevate a PIREP to urgent (UUA). Moderate turbulence or light icing do not.
Misreading turbulence frequency descriptors: Candidates mix up the thresholds. Occasional is less than one-third; intermittent is between one-third and two-thirds; continuous exceeds two-thirds.
Assuming pilot reports are official forecasts: A PIREP is an observation valid for a specific location, altitude, and time. It does not guarantee conditions elsewhere on the route, and it ages rapidly — particularly for convective turbulence, which can change within minutes.
Overlooking aircraft type bias: A light turbulence report from a large jet may represent moderate or even severe turbulence for a small general aviation aircraft. Always consider the /TP element when interpreting a PIREP.