Alternate at the Edge: Destination Forecast, Fuel, and Known Icing
You are planning an IFR flight in a Piper Archer with 48 gallons usable and a fuel burn of 10 gallons per hour. The estimated time en route is 2 hours 15 minutes. The destination TAF for your ETA plus or minus 1 hour forecasts BKN018, 6 SM visibility, with a TEMPO of 1,500 OVC and 2 SM. The only suitable alternate, KCCC, has an ILS runway 9 and a forecast of 700 OVC and 2 SM. The MEA is 6,000 MSL; your planned altitude is 9,000 MSL. The freezing level is forecast at 8,000 MSL, and a PIREP reports light rime icing at 7,000 MSL. The Archer is not approved for flight into known icing. Fuel at departure is 48 gallons. KCCC is 25 minutes from the destination. You hold a current instrument rating, and the airplane is IFR-certified.
1. Is an alternate required, and does KCCC meet the alternate weather minimums? Show your reasoning.
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An alternate is required. Under 14 CFR 91.169, an alternate is required if, for the period from 1 hour before to 1 hour after the estimated time of arrival, the destination ceiling is forecast below 2,000 feet or the visibility is forecast below 3 SM. The destination forecast is BKN018, which is a ceiling of 1,800 feet, already below 2,000 feet. The TEMPO of 1,500 OVC and 2 SM reinforces the need for an alternate.
KCCC qualifies if the 700 OVC and 2 SM forecast applies during the required window. KCCC has an ILS, so it is a precision approach. Under 91.169(c)(1), the alternate minimums for a precision approach are 600-foot ceiling and 2 SM visibility. A ceiling of 700 feet and visibility of 2 SM meet those minimums. If the 700/2 is only a temporary condition and the prevailing forecast is worse, the alternate would not qualify. Also confirm that no alternate-airport exception applies; here a suitable alternate exists, so the exception for no available alternate does not apply.
2. Does the fuel load meet 14 CFR 91.167? Calculate the required fuel.
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Because an alternate is required, the fuel must include destination, alternate, and 45 minutes of reserve at normal cruise. Destination fuel: 2.25 hours times 10 gallons per hour equals 22.5 gallons. Alternate fuel: 25 minutes is 0.42 hour, times 10 equals about 4.2 gallons. Reserve: 45 minutes is 0.75 hour, times 10 equals 7.5 gallons. Total required is 22.5 plus 4.2 plus 7.5, or 34.2 gallons. The aircraft has 48 gallons usable, so the flight is legal with about 13.8 gallons of margin.
That margin is not a license to ignore wind, delays, or a changed alternate. If the destination requires a hold or the alternate forecast deteriorates, recalculate. Also remember that 91.167 is a minimum; prudent planning would use a higher personal reserve, especially with icing and a mountain MEA. The calculation should be shown to the student as a template, not just a yes-or-no answer.
3. What do you do about the icing forecast and PIREP? Can you make the flight as planned?
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No. The planned altitude of 9,000 MSL is above the forecast freezing level of 8,000 MSL, and a PIREP reports light rime icing at 7,000 MSL. The Archer is not approved for flight into known icing. Light rime is still icing, and the report suggests the freezing level may be lower or the moisture deeper than the forecast. Planning to fly at 9,000 would place the flight in conditions where icing is forecast and reported.
Options are to plan a lower altitude that keeps the aircraft clear of visible moisture and freezing temperatures, provided terrain and the MEA allow it; to delay until conditions change; or to cancel. At 6,000 MSL the MEA is acceptable, but the PIREP at 7,000 means you need current temperature and moisture information before assuming 6,000 is clear. If you cannot stay clear of known icing, do not go. This is a risk-management decision under 14 CFR 91.9 and 91.13 and the aircraft limitations, not merely a forecast-reading exercise. Brief the student on the difference between 'forecast icing' and 'known icing' and why a non-FIKI airplane does not belong in either.