Partial Panel in IMC After an Unusual Attitude
You are in IMC at 6,000 ft on an IFR clearance, in smooth air, when the attitude indicator begins to tumble and the heading indicator slowly precesses. You have a vacuum-driven attitude and heading indicator and electric turn coordinator. The pitot-static system is working: airspeed, altimeter, and vertical speed are reliable. ATC has just issued a crossing restriction to be at 4,000 ft in 4 minutes and then a heading of 090 for sequencing. You are 18 NM from a busy terminal area, and the controller's transmissions are rapid. There is embedded light rime icing reported between 5,000 and 7,000 ft.
1. What is your first radio call, and why does it come before troubleshooting?
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First call: "[Callsign], partial panel - attitude and heading indicators failed - request vectors and relief from the crossing restriction." State the equipment problem and what you can and cannot do. This comes first because ATC's crossing restriction and heading change assume full-panel capability; accepting them silently may commit you to a rate of descent or a turn you cannot reliably fly. Declaring partial panel gets you relief from the restriction, vectors and traffic separation, and a known state for the controller. Keep it short and standard; do not troubleshoot gyros while a busy controller awaits a readback.
2. How do you fly the airplane and manage the icing and traffic constraints with the instruments you have?
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Use the pitot-static instruments plus the turn coordinator as your primary reference:
- Airspeed and vertical speed for pitch; altimeter for level-off.
- Turn coordinator for wings-level and standard-rate turns; time the turns (a standard-rate turn is 3°/sec, so 30 seconds ≈ 90°).
- Cross-check against the magnetic compass with timed, level, unaccelerated reads to avoid dip errors. Icing: request a climb or descent out of the 5,000–7,000 ft band as soon as practical, but do not accept a rapid descent you cannot control partial panel. Ask ATC for a block altitude or a vector to a lower MEA. Traffic: accept vectors but request traffic advisories and keep your transponder on; in a busy terminal area, partial panel plus icing means you should ask for the nearest suitable airport rather than continuing the full route.
3. When should you declare an emergency rather than continue as a priority?
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Declare when the situation exceeds your ability to safely continue: if you lose another instrument, if icing degrades performance or airspeed indications, if you cannot maintain assigned altitude within tolerance, or if you become disoriented. The phrase "declaring an emergency" unlocks priority handling, and you should not hesitate because you feel the situation is "not that bad." A partial panel in IMC in a busy terminal area with icing is already a serious degrade; the threshold for declaring is low. If you declare, state intentions plainly: "Request immediate vectors to the nearest airport, we are partial panel and picking up icing." Then fly the airplane first and let ATC fit you into the sequence.