Night IFR Approach Below Minimums With a Failed Pitot Heat
You are flying a twin-engine turboprop on an night IFR approach to a Canadian airport. The approach is an ILS to runway 27, decision altitude 250 ft AGL, visibility 1/2 sm. Weather is 300 ft overcast, 1/2 sm visibility, wind 270° at 8 knots. On descent through 4,000 ft, the pitot heat caution illuminates, and your airspeed indicator begins to read erratically - first high, then low. You have 30 minutes of fuel above reserves. The missed approach is a climb to 3,000 ft and a hold at a VOR 12 nm away.
1. What is the hazard and what should you do immediately?
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A failed pitot heat with an erratic airspeed indicator means the pitot tube is likely icing. The airspeed indicator is unreliable, and you cannot safely fly an instrument approach that depends on accurate airspeed. Erratic readings - high then low - are classic for a blocked pitot tube: if the pitot is blocked but the static port is clear, the indicator behaves like an altimeter, climbing as you climb and descending as you descend. If the static is also blocked, the indicator freezes at the last value.
Immediate actions: disengage the autopilot if it is using airspeed, maintain aircraft control by attitude and power, and cross-check with the standby airspeed indicator, GPS ground speed, and engine instruments. Turn on pitot heat if it is not already on and see if the indicator recovers. Declare the situation to ATC and request a climb to warmer air if icing is suspected.
Do not continue the approach. An ILS to 250 ft AGL with an unreliable airspeed indicator is unsafe. Fly the missed approach using attitude, power, and vertical speed, and request vectors to a hold or a diversion to an airport with better weather and warmer temperatures.
2. If the airspeed indicator does not recover, what is your plan?
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If the indicator does not recover, treat the aircraft as having an unreliable airspeed system. Fly by attitude, power setting, and known pitch-and-power combinations for the aircraft. Use GPS ground speed and vertical speed as cross-checks, and use the standby airspeed indicator if it is independent and reliable.
Plan: climb to an altitude above the freezing level where the ice can melt, or to a warmer layer if one exists. If the pitot remains blocked, divert to an airport with VFR conditions or at least a much higher ceiling and visibility, and plan a long, stabilized approach with a generous speed margin. Request a precision approach with vertical guidance if available, but fly it by attitude and power, not by airspeed.
Fuel: 30 minutes above reserves limits your options. Declare minimum fuel or an emergency if needed, and choose the nearest suitable airport with good weather. Do not attempt the original approach. If no suitable airport is within fuel range, declare an emergency and request priority handling to the nearest airport with the best conditions.