The PIREP, the Icing Report at Eight Thousand That Nobody Filed, and the Real-Time Weather Data Only Other Pilots Can Give You

PIREPs - pilot reports - are the only source of real-time, altitude-specific weather information generated by actual pilots in the air. Every other layer of your weather briefing is model-based or ground-based. A PIREP is a first-hand account of what a specific aircraft encountered at a specific altitude at a specific time. Understanding how to read them, weight them in context, and contribute to the system yourself is a core aeronautical decision-making skill.

What Is a PIREP and How Is It Formatted?

A PIREP is a coded weather observation made by a pilot in flight. They come in two forms:

• UA - the routine pilot report
• UUA - the urgent pilot report, reserved for severe turbulence, severe icing, tornadoes, waterspouts, or hail

The format follows a standard sequence: location identifier (nearest VOR or airport), time in Zulu, altitude in hundreds of feet (FL080 = 8,000 feet), aircraft type, then observed conditions - sky condition, weather, temperature, and winds - in that order, reported only when the pilot actually observed them. Not every PIREP includes every field. Pilots report what they see.

How Do You Interpret Turbulence Intensity in a PIREP?

The turbulence scale used in PIREPs is standardized across four levels:

• Light turbulence - slight, erratic changes in attitude and altitude. Passengers notice it but remain comfortable and can move around the cabin.
• Moderate turbulence - the aircraft remains in positive control, but conditions are uncomfortable. Unsecured objects move. Passengers are pushed against their seatbelts. Walking the cabin is difficult.
• Severe turbulence - large, abrupt changes in attitude and altitude. The aircraft may momentarily be out of control. Occupants are violently thrown against their restraints. Declaring an emergency may be appropriate.
• Extreme turbulence - structural damage territory. Rare, but it has brought airplanes down.

The turbulence scale is subjective. It reflects how the reporting pilot experienced conditions in their specific aircraft. A Cherokee pilot reporting moderate turbulence is describing what those conditions felt like in a relatively slow, low-wing-loading airplane at lower altitude. The same airmass might feel like light chop to a Cirrus SR22 at a higher airspeed and wing loading, or like a gentle washboard to a turboprop crew who routinely fly bumpy air.

This doesn’t mean you ignore the report - it means you contextualize it. A Piper Navajo report is more directly applicable to a Beechcraft Baron than an Airbus A320 report is. A Cessna 172 report tells you specifically what the low, slow world looks like at that altitude.

Timing matters as much as aircraft type. PIREPs age. In a stable, slowly-changing airmass an older report may still be useful. In a rapidly evolving situation - approaching frontal passage, building convection - a report from 90 minutes ago may be essentially irrelevant.

How Do You Interpret Icing Intensity in a PIREP?

Icing intensity follows a similar four-tier scale:

• Trace icing - ice is perceptible but accumulates slowly. Deicing equipment handles it easily. For aircraft with no deicing capability, trace icing sustained over a long flight can still become a factor.
• Light icing - accumulation rate requires occasional use of deicing equipment to prevent dangerous buildup. Without equipment, exit these conditions.
• Moderate icing - deicing equipment must run continuously. Without it, the accumulation rate is hazardous even over short periods. A non-deiced aircraft has no business in moderate icing. Period.
• Severe icing - accumulation rate exceeds what deicing equipment can manage. Immediate action is required. This is an emergency for any aircraft.

Ice type matters independently of intensity:

• Rime ice - white, opaque, rough. Forms when supercooled droplets freeze rapidly on contact. Tends to accumulate on leading edges.
• Clear ice - the dangerous one. Forms more slowly, conforms to the shape of the airfoil, is heavier, and is far harder to remove mechanically.
• Mixed icing - rime and clear together, common in real-world conditions, and tends to be unpredictable.

An icing PIREP delivers something no forecast can: a pilot was at a specific altitude, at a specific location, at a specific time, and this is what actually happened. That’s irreplaceable.

How Do PIREPs Fit Into a Complete Weather Briefing?

PIREPs are one layer in a stack, not a standalone source. A complete pre-flight weather picture includes surface analysis, prog charts, METARs, TAFs, winds aloft, AIRMETs, SIGMETs, and PIREPs. Each layer answers a question the others can’t.

The AIRMET for icing (AIRMET Zulu) indicates a reasonable probability of icing in a broad geographic area based on atmospheric modeling. A PIREP reports what a pilot actually encountered. These answer different questions:

• AIRMET: What is likely?
• PIREP: What happened?

When an AIRMET indicates possible icing and PIREPs along your route are consistently reporting negative - no icing observed - that’s meaningful context. Maybe the atmospheric models ran slightly warm. You don’t discard the AIRMET on the strength of a few pilot reports, but you have information you wouldn’t otherwise have.

When an AIRMET indicates possible icing and multiple PIREPs from different aircraft at different altitudes all report light to moderate rime, the atmosphere is confirming the forecast. Take that very seriously.

The scenario that demands the most caution: no PIREPs at all along your route. Absence of a PIREP is not a report of clear conditions. It’s the absence of information - and that’s a different thing entirely. If you’re flying into an area covered by an active icing AIRMET with zero PIREPs along the route, you’re flying into unobserved conditions, not a confirmed safe path.

How Do You Actually File a PIREP?

The simplest method is by radio. 122.2 MHz is a common Flight Service frequency with remote outlets across the country. Center and approach controllers will also accept your PIREP and relay it to flight service - tell them “I’d like to file a PIREP” and they’ll prompt you through the format. You can also file through Leidos Flight Service by phone, or through ForeFlight and other EFB platforms.

Information to provide, in order:

1. Location - nearest VOR or fix
2. Time in Zulu
3. Altitude
4. Aircraft type
5. Observed conditions - turbulence intensity and altitude range, icing type and intensity, sky condition, temperature at altitude, winds if known

You do not need to be instrument rated to file a PIREP. VFR pilots file them, and they carry real value. Found smooth air at 4,500 feet over a ridge that was forecast to be bumpy? File it. Topped out at 9,000 feet and found clear blue above the overcast? File it. The next pilot building a go/no-go decision for that same corridor needs to know.

Your report enters the system exactly as you described it and is distributed to other pilots the same way a commercial crew’s report is. The system trusts that you accurately observed what you reported. Your job is to be accurate and use correct terminology so the report is interpretable.

Why Does General Aviation Owe the System More PIREPs?

Commercial traffic operates at high altitudes. The layer between 3,000 and 6,000 feet is often flown exclusively by general aviation aircraft - and when those pilots don’t file, that layer goes entirely unobserved. A student pilot on a cross-country who encounters light rime icing at 6,000 feet and calls it in is giving low-altitude pilots something no other data source can provide.

The expectation to contribute is built into FAA guidance and the culture of aviation. The Airman Certification Standards make explicit for instrument pilots that sound aeronautical decision-making means using all available information - reading PIREPs carefully, understanding their limitations, and feeding back into the system yourself. The principle applies at every certificate level.

The weather briefing you used this morning had PIREPs in it because other pilots flew that route and took sixty seconds to call it in. The pilots flying tomorrow have the same need.

Key Takeaways

• UA is a routine PIREP; UUA is urgent - reserved for severe turbulence, severe icing, tornadoes, waterspouts, or hail.
• Turbulence and icing intensities are subjective. Always consider the reporting aircraft type relative to what you’re flying.
• PIREPs age quickly in dynamic weather. A report from 90 minutes ago may be meaningless near frontal passage or building convection.
• Absence of PIREPs is not a clear-weather report. It’s a gap in information - especially dangerous when an active AIRMET is in effect for your route.
• Any pilot - VFR or IFR, student or ATP - can and should file PIREPs. General aviation is often the only coverage in the low-altitude layer where it’s needed most.