Icing on the Approach: Continuing or Diverting at Minimum Fuel
You are inbound on an ILS to Runway 27 at a mountain-adjacent airport. ATIS reports wind 260/12, visibility 1 1/2 SM in light freezing drizzle, ceiling 400 ft overcast, temperature -2°C, dewpoint -3°C. The ILS DA is 200 ft AGL and the approach is authorized for Category I only. Your aircraft is approved for flight into known icing but has no anti-ice protection on the tail surfaces. You have 35 minutes of fuel above your final reserve, and the alternate is 40 minutes away with a forecast of 800 ft ceiling and 2 SM visibility. Freezing drizzle has been reported for the last 20 minutes.
1. Assess the icing hazard and decide whether to continue the approach.
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Freezing drizzle at -2°C is a serious signal. Drizzle implies supercooled liquid water droplets in a narrow temperature band, and those droplets freeze on impact and can accrete rapidly, especially on unprotected surfaces. Your aircraft has no tail anti-ice, so tail-plane icing is the critical risk: it can cause a pitch upset on approach that is difficult to recover from at low altitude.
The reported conditions - freezing drizzle for 20 minutes, temperature within 1°C of dewpoint - mean the icing environment is established, not transient. Continuing to DA in these conditions with an unprotected tail is a poor risk trade. The safer decision is to discontinue the approach, advise ATC, and divert to the alternate, where the forecast is above approach minimums and the temperature is likely warmer.
2. If you did continue and went missed at DA, what would you expect and how would you fly it?
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At DA with the runway not in sight, you would initiate the published missed approach immediately: full power, pitch to the missed approach climb attitude, and configure as the procedure requires. In icing, expect degraded climb performance and possible airframe buffet. Do not retract flaps below the procedure's minimum until a positive climb is established and airframe ice has begun to shed.
Because the missed approach may route you back into the same icing layer, plan to climb through it quickly and request a heading or altitude that gets you into warmer air or clear air. Report the missed approach and your icing encounter to ATC so following traffic is warned. If climb performance is marginal, declare an emergency early rather than waiting until you are below the procedure's climb gradient.
3. How does the fuel situation affect your decision?
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Thirty-five minutes above final reserve is tight but not critical if you divert now. The alternate is 40 minutes away, which means you would arrive with the final reserve intact only if the diversion is prompt and the approach at the alternate is not delayed. If you fly the approach to DA and go missed, you will have burned additional fuel and will be diverting with less margin.
The correct planning is to make the divert decision before commencing the approach, not at DA. With 35 minutes above reserve and a 40-minute alternate, you have essentially one attempt at the alternate and no room for a second approach. That reinforces discontinuing now. If you were to continue, you should declare minimum fuel to ATC and have a second alternate identified.