Vacuum Failure at Night in IMC

The vacuum system has failed, and the attitude indicator is lying to you.

Confirmation is by disagreement plus an independent cross-check:

• Suction 3.2 in Hg is below the green arc - the source is sick, and both the AI and DG are vacuum-driven.
• The AI shows a shallow left bank, but the electric turn coordinator shows wings level, and the altimeter, VSI, and airspeed are steady. A real bank would produce a turn, a heading change, and a VSI deviation. The AI disagrees with three independent instruments.
• The DG drifting 15 degrees in two minutes is the same failure, not a separate one.

Next 60 seconds: ignore/cover the AI and DG so you stop chasing them. Trim for level flight, set climb or cruise power as cleared, use small control pressures, and put a light touch on the yoke. Turn pitot heat on. Fly partial panel: the turn coordinator is your bank reference but only reliable up to standard rate, so make all turns at standard rate and use timed turns (3 deg/sec, 10 sec = 30 deg), cross-checking the GPS ground track for a heading substitute. Use the magnetic compass only in smooth air. The GPS gives you a usable wind-corrected track and groundspeed - a real advantage here.

Legally you are already outside the equipment rules; the question is whether continuing is the lower-risk option.

§91.205(d) requires, for IFR, a gyroscopic bank-and-pitch indicator and a gyroscopic direction indicator. Both are now inoperative. The airplane is no longer IFR-airworthy, so continuing under IFR is a deviation permitted only by §91.3(b) - an in-flight equipment failure you did not cause, with the deviation limited to what is necessary. Practically that means you must declare it and explain yourself to ATC, not just carry on quietly.

Can the ILS be flown partial panel? Yes - turn coordinator for bank, localizer and glideslope for pitch/power. But weigh the actual configuration: single pilot, night, no autopilot, 500 ft overcast to a 200-1/2 decision altitude, with a missed approach that will be flown partial panel in cloud.

Contrast the alternative: 20 minutes back to 3,000 broken / 10 SM, where the flight can end in visual conditions and the failure stops mattering. My call: tell ATC 'partial panel,' request vectors toward the VMC airport, and continue IFR only as long as it takes to get there - unless fuel or terrain makes the destination clearly safer, in which case brief a hard floor and expect to go around rather than press a bad approach.

Reduce workload, simplify the geometry, and assume the missed approach.

• Long final. Ask for vectors to a 20-30 NM final. That gives you time to configure, set power, and stabilize instead of arriving at the OM already behind the airplane.
• No-gyro handling. With the DG unusable you cannot give ATC accurate headings. Request a no-gyro approach (ATC calls 'turn'/'stop turn,' and you turn at standard rate) or, if available, an ASR/PAR. Say the words on initial contact, not at the final approach fix.
• Attitude reference. On the ILS, the localizer and glideslope are your attitude instruments - wings level on the localizer, pitch on the glideslope - with known power settings and configuration established early.
• Missed approach brief. Straight-ahead climb, wings level, best rate, using airspeed and VSI; climb to the MSA before any turn, and treat any turn as a timed standard-rate turn with the GPS ground track as backup. At 500 ft overcast, expect to go missed, so brief the diversion before the FAF.
• Personal minimums. No circling approaches, no circling in any form, and a firm commitment to break off if not stabilized by 500 ft above minimums.