Icing and Convection on the Laoag Route
You are flying a Cessna 172S IFR from Manila to Laoag at 9,000 ft. The OAT is −2°C in cloud, and the freezing level is 7,000 ft. A PIREP reports moderate rime icing between 8,000 and 10,000 ft. You see a thin line of rime on the struts, and the airspeed has dropped 5 kt in the last 5 minutes. The MEA is 7,000 ft; terrain west of the route rises to 6,500 ft. A convective SIGMET is active for a line of thunderstorms 25 nm ahead, tops FL380, moving east at 15 kt. Laoag is 1,200 ft overcast with 5 km visibility; Clark is behind you at 1,500 ft overcast with 8 km. Fuel remaining is 2+15.
1. What is the immediate threat, and what actions do you take for the icing?
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The immediate threat is icing, not destination weather. A 172 is not approved for flight into known icing, and 5 kt of airspeed loss plus visible rime at −2°C means you are accumulating ice.
Request 6,000 ft: it is below the 7,000 ft freezing level, so the temperature should be above 0°C and the ice should melt, and it is above the 6,500 ft terrain west of the route-but confirm the MEA/MVA and terrain clearance with ATC before descending, because the published MEA is 7,000 ft. If a lower altitude is not available, turn back or climb only if the temperature is clearly warmer above a shallow layer. Do not wait for a full load of ice.
Advise ATC of the icing and request a deviation or altitude change.
2. The convective line is 25 nm ahead. Do you continue to Laoag or turn back to Clark?
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With ice on the airframe, a 172 has degraded climb performance and a higher stall speed, so penetrating a convective line is unacceptable. The line is 25 nm ahead and moving east toward you; even a deviation may not clear it, and embedded storms in IMC are invisible.
The safer decision is to turn back to Clark, which is behind you, 1,500 ft overcast with 8 km, and where you can land and have the ice inspected. Continuing to Laoag means flying through or around the line with less performance and only 2+15 of fuel.
If you divert, advise ATC immediately, request a heading away from the line, and avoid a tight turn that increases load factor and stall speed with ice. Do not climb into the storm tops.
3. What PIREP and ATC report should you make?
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File a PIREP: "Moderate rime icing, 8,000–9,000 ft, temperature −2°C, Cessna 172, 5 kt airspeed loss, encountered at [time] UTC, 20 nm northeast of [fix]." Ask ATC to relay it.
Also report the convective line if you have radar or visual evidence, and request a deviation. If you divert, request a clearance to Clark and state the reason-icing and convective activity.
Keep the report factual: type, intensity, altitude, temperature, and effect on the aircraft. A PIREP is not a sign of weakness; it is the fastest way to warn other crews and to get ATC to help you.