IFR Emergencies

Partial Panel Flying

Flying with reference only to the instruments that remain operational after one or more fail. The skill underlying every IFR emergency.

• If you understand each instrument independently, the loss of one or two does not change the way you fly — your scan adapts to use what's left
• You are required to report malfunctions of navigational, approach, or communication equipment in flight
• Advise ATC of the problem and the level of assistance needed. Example: "Portland Approach, Helicopter 969MH, experiencing failed turn coordinator, continuing IFR unimpaired, no assistance required."
• Don't omit the instrument from your verbal report — but do deliberately omit it from your scan once confirmed failed. A failed instrument that's still being scanned is a distraction.

Attitude Indicator Failure

The most disorienting failure in IMC — the AI is the centerpiece of every common scan. If suspected:

• Make small control inputs and watch the response — does the AI move appropriately, or is it stuck/tumbling/tilted?
• Try resetting the relevant circuit breaker
• If confirmed failed, cover or omit it from the scan — staring at it is worse than ignoring it
• Cross-check pitch using altimeter + VSI + airspeed; bank using turn coordinator + heading indicator
• Notify ATC and request vectors to VMC if available

Heading Indicator Failure — No Compass Turns

The heading indicator (DG) is a gyro that drifts. It needs to be cross-checked against the magnetic compass every 15 minutes.

• Suspect a failed DG if heading adjustments aren't producing the expected effect on nav instruments
• If failed, fall back on the magnetic compass — but compass turns have errors:
  • UNOS — Undershoot North, Overshoot South: When turning to a northerly heading, lead the rollout by 15° + half your latitude. When turning to a southerly heading, lag the rollout by the same amount.
  • ANDS — Accelerate North, Decelerate South: Acceleration on an east/west heading shows a turn toward north on the compass; deceleration shows a turn toward south. Don't chase it.

Vacuum / Pitot-Static Failure Groups

Most older IFR helicopters group instruments by power source. Knowing which fail together is the first step in diagnosis:

• Vacuum failure: Loses attitude indicator and heading indicator (both gyros, both vacuum-driven). Turn coordinator survives — it's electric. Cross-check vacuum gauge during preflight and routinely.
• Pitot blockage: ASI freezes at the airspeed at impact (or behaves like an altimeter if both pitot and drain are blocked). Altimeter and VSI unaffected.
• Static blockage: ASI, altimeter, and VSI all behave erratically. Altimeter freezes; VSI shows zero; ASI under-reads at higher altitudes. Use the alternate static source (will read slightly lower altitude due to lower cabin pressure). If no alternate source, break the VSI glass — VSI is non-required, and breaking it provides static air to the other two.

Lost Communications — Squawk Codes

Three transponder codes every IFR pilot has to know cold:

• 7500 — Hijack ("been hijacked")
• 7600 — Lost comm ("radio in a fix")
• 7700 — Emergency ("going to heaven")

Mnemonic: 5 hijacked, 6 in a fix, 7 to heaven.

Lost Communications — Procedures (14 CFR § 91.185)

If in VMC when comm fails: Continue VFR and land as soon as practicable.

If in IMC, fly the route — AVE F:

• A — Assigned — Fly the route last assigned by ATC
• V — Vectors — If being vectored, fly direct from the present position to the fix/route specified in the vector clearance
• E — Expected — Fly the route ATC has advised you may expect (in case the assigned clearance hasn't been received yet)
• F — Filed — Fly the route filed in your flight plan

Fly the altitude — MEA:

• M — Minimum IFR altitude for the route segment
• E — Expected altitude (per ATC's "expect" clearance)
• A — Assigned altitude
• Use the highest of the three for each route segment

Squawk 7600. Begin the approach at your destination as close as possible to your filed/assigned ETA (or EFC time if holding). Land. Call FSS or the relevant ATC facility on a landline.

Light Gun Signals (Tower in Sight, Comm Lost)

• Steady green: Cleared to land (in the air) / cleared for takeoff (on the ground)
• Flashing green: Return for landing (in the air) / cleared to taxi (on the ground)
• Steady red: Give way to other aircraft and continue circling (in the air) / stop (on the ground)
• Flashing red: Airport unsafe, do not land (in the air) / taxi clear of runway in use (on the ground)
• Flashing white: Return to starting point on airport (ground only)
• Alternating red/green: Exercise extreme caution (any time)

Engine Failure in IMC

The worst-case helicopter emergency. No reliable warning of when engines will fail — and no guarantee they won't fail at night or in fog. The ground is invisible until it hits you.

Constant Attitude Autorotation: The IMC / night version of an autorotation. Removes the flare from the maneuver because you can't time it.

• Lower-than-normal airspeed: about 35–40 KIAS plus half the windspeed, helicopter facing into the surface wind
• Maintain that airspeed all the way down to the moment of pulling collective
• If margin is needed, err slightly higher in airspeed — never slower
• At about 50 ft AGL (in daylight) or when the landing light first illuminates the ground (at night), begin feeding in collective — slowly at first, then as rapidly as needed
• Do not flare. There isn't enough kinetic energy at this airspeed to change the flight path with a flare — it would only change the attitude on impact
• Accept the slight forward speed at touchdown

Practiced rarely (it's hard on the helicopter), but understanding the technique is what separates a survivable IMC engine failure from a fatal one.

IIMC — Inadvertent IMC

VFR pilot enters IMC unintentionally. The leading cause of fatal accidents in helicopter EMS, and a real risk in mountain and night ops. The procedure must be reflexive — no time to think.

1. Maintain aircraft control — wings level, climb attitude, target airspeed
2. Climb — to a known safe altitude above terrain (look up your area's MSA)
3. Course — turn toward known VMC or toward an emergency airport
4. Communicate — declare emergency, request ATC assistance
5. Comply — with ATC instructions

Practice IIMC recovery in training until you can execute it without conscious thought. The first three actions take five seconds — every second of hesitation costs altitude or aircraft control.

Airframe Icing

Three conditions must coexist for ice to form:

1. Temperature — between 0°C and -20°C is the prime band
2. Moisture — visible moisture in the air (cloud, precipitation)
3. Droplet size — large supercooled droplets accrete more aggressively than fine ones

Anti-ice vs. de-ice: Anti-ice prevents ice from forming (heated leading edges, weeping wing). De-ice removes ice that has already formed (boots).

Types of Ice

• Clear ice: Glossy, transparent. Forms 0°C to -10°C in large supercooled droplets at higher airspeeds. Slow freezing produces a dense, hard, smooth coating that follows the airfoil shape — and that's what makes it the most dangerous type. Hard to see, hard to break off.
• Rime ice: Rough, milky, opaque. Forms -10°C to -20°C from rapid freezing of supercooled droplets — air gets trapped, giving it the porous opaque appearance. Typical in stratus clouds. Brittle and easier to remove than clear ice.
• Mixed ice: -8°C to -15°C — combination of clear and rime characteristics. Hardest to identify in flight.
• Frost: Thin layer of crystalline ice. Forms on clear, calm nights when the airframe surface temperature drops below freezing and dew point. Also when descending from cold air into warm humid air. Even thin frost can disrupt airflow enough to cost lift.

Icing Intensity Classification

• Trace: Perceptible, no significant accumulation. Hazardous if anti-ice/de-ice is unavailable.
• Light: Significant accumulation over > 1 hour of flight. Occasional use of anti-ice/de-ice prevents accumulation.
• Moderate: Even short encounters become hazardous. Use of anti-ice/de-ice is necessary, or divert.
• Severe: Anti-ice/de-ice fails to control the hazard. Immediate diversion required.

Most light helicopters are not certified for flight into known icing. If you encounter icing, your action plan is: (1) reverse course or change altitude to exit, (2) declare if needed, (3) land.