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Instrument rating · ACS IR.II.A

Aircraft Systems for IFR

IFR puts the airplane in visible moisture and asks more of its systems. This lesson covers the ones that matter most: ice protection, flight controls and the autopilot.

Why this one matters

Instrument pilots meet ice and automation surprises that VFR pilots avoid by staying out of clouds. Ice changes how the airplane flies before it changes how it looks, and an autopilot that is quietly fighting ice or flying the wrong mode lets a pilot fall behind. Knowing your airplane’s systems and limits turns those surprises into early decisions.

Can’t miss

  • •Anti-ice prevents ice from forming (pitot heat, heated windshields, prop anti-ice); deice removes ice that has formed (boots). Know which your airplane has.(Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Aircraft Systems)
  • •Most trainers are not approved for flight into known icing. The POH/AFM limitations section says whether yours is.(Your airplane's POH/AFM and supplements)
  • •Turn pitot heat on before entering visible moisture near or below freezing. A blocked pitot tube makes the airspeed indicator wrong.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • •Even a thin layer of ice on the wing raises the stall speed and can cause a stall with no usual warning. Exit icing at once: a 180° turn, a climb to colder air or above the tops, or a descent to warmer air. If the clearance blocks your exit, declare an emergency and take it. Freezing rain or drizzle: exit immediately, even in an airplane approved for known icing.(AC 91-74B, Pilot Guide: Flight in Icing Conditions; 14 CFR 91.3)
  • •Induction icing is a different problem from structural icing: carburetor ice forms from venturi and fuel-evaporation cooling, well above freezing (up to about 21°C/70°F) in humid or clear air, especially at low power. Signs: an RPM or manifold-pressure drop and roughness. Full carb heat per the POH; expect more roughness briefly as the ice melts. Fuel-injected engines have alternate air for a blocked filter.(Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Aircraft Systems)
  • •An autopilot can hide the effects of ice by trimming against them, then let go in an upset. Know the POH guidance for the autopilot in icing.(AC 91-74B, Pilot Guide: Flight in Icing Conditions)
  • •Know every way to disconnect the autopilot, its modes, and what it will do next. Automation lowers workload only when you stay ahead of it.(Advanced Avionics Handbook (FAA-H-8083-6))

What you should know

Ice protection K1 · R1 · R2

  • Structural icing needs visible moisture and a temperature at or below freezing on the airframe. Freezing rain and drizzle are the most dangerous.(AC 91-74B, Pilot Guide: Flight in Icing Conditions)
  • Anti-ice systems prevent ice; deice systems remove it. Boots are deice: follow the POH/AFM. Without specific guidance, activate them at the first sign of ice and cycle them early and often; modern boots don't "ice-bridge", so waiting for ice to build is not the technique.(AC 91-74B, Pilot Guide: Flight in Icing Conditions; Your airplane's POH/AFM and supplements)
  • Pitot heat protects the airspeed indicator. Fuel vents and the static ports can ice too; know where yours are and check them on preflight.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • Pitot-static blockages: pitot blocked with the drain open, airspeed drops toward zero; pitot and drain both blocked, the airspeed acts like an altimeter (up in a climb, down in a descent); static blocked, the altimeter freezes, the VSI reads zero and the airspeed is right only at the altitude where it blocked.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • Approval for flight into known icing is in the POH/AFM. Equipment that helps exit ice is not an approval to fly in it.(Your airplane's POH/AFM and supplements)
  • If you pick up ice: tell ATC, ask for a different altitude or route, and get out. Keep extra airspeed on the approach.(AC 91-74B, Pilot Guide: Flight in Icing Conditions)
  • Tailplane icing: the thinner tail collects ice faster than the wing. Extending flaps can stall the tail: a sudden nose-down pitch, light or buffeting elevator. Recovery is the opposite of a wing stall: retract the flaps to the previous setting, pull back, and set power and speed per the POH. With ice aboard, land with minimum flaps and extra airspeed.(AC 91-74B, Pilot Guide: Flight in Icing Conditions)

Flight controls and the autopilot K2 · R3

  • Flight controls: primary (ailerons, elevator, rudder) by cables or pushrods, secondary (flaps, trim) mechanical or electric. Check them free and correct on preflight. Ice changes their feel and authority: heavier forces, less response, and tail ice can reduce elevator effectiveness.(Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Aircraft Systems)
  • Runaway electric trim, typically: hold the controls firmly, press and hold the autopilot/trim disconnect, pull the trim circuit breaker or switch it off, then retrim by hand. Your POH gives the exact order.(Your airplane's POH/AFM and supplements)
  • Know the autopilot’s modes (heading, nav, altitude, vertical speed, approach), how to preflight it, and every way to disconnect it: typically the disconnect button on the yoke, the autopilot button on the panel, the trim switch (on many systems), and the autopilot circuit breaker or master switch.(Advanced Avionics Handbook (FAA-H-8083-6); Your airplane's POH/AFM and supplements)
  • Say what the autopilot is doing and what it will do next. Check the mode annunciations after every change.(Advanced Avionics Handbook (FAA-H-8083-6))
  • Automation helps single-pilot IFR most when you use it to reduce workload, and you are always ready to hand-fly.(Risk Management Handbook (FAA-H-8083-2A))

Scenarios

Decide what you would do first, then see the worked answer.

The forecast shows tops at 8,000 feet and a freezing level of 5,000 feet. Your trainer isn’t approved for known icing, and the route needs 7,000.

Is this flight a good idea? See the worked answer

No: climbing through and cruising in cloud below freezing is flight into known icing, prohibited by the limitations under 91.9(a). Go only if the whole route, climb and descent included, stays out of cloud above the freezing level.

AC 91-74B, Pilot Guide: Flight in Icing Conditions; 14 CFR 91.9

On autopilot, the airspeed is slowly dropping at constant power and altitude.

What could be happening? See the worked answer

Ice may be adding drag. Check for ice, take control if needed, and exit the conditions.

AC 91-74B, Pilot Guide: Flight in Icing Conditions

After a mode change the autopilot starts a climb you didn’t expect.

What do you do? See the worked answer

Fly the airplane: disconnect if needed, return to the assigned altitude, then sort out the mode.

Advanced Avionics Handbook (FAA-H-8083-6)

Common mistakes

  • Forgetting pitot heat.

    The airspeed indicator fails in ice.

    Instead: Pitot heat on before visible moisture near freezing.

  • Treating ice protection as approval.

    Equipment helps you exit, not stay.

    Instead: Check the POH limitations.

  • Not knowing the disconnects.

    A wrong autopilot input can’t be stopped fast.

    Instead: Know every disconnect before you fly.

Now train it

Say it out loud, hear it asked, and take the quick check in this lesson’s practice pack. It tracks your shaky spots.

Train this lesson

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Sources

  • AC 91-74B: Flight in icing conditions
  • Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C): Aircraft systems
  • Instrument Flying Handbook (FAA-H-8083-15B): Flight instruments
  • Advanced Avionics Handbook (FAA-H-8083-6): Automation and autopilots
  • Instrument Rating ACS (FAA-S-ACS-8C): Area II

Study aid, not FAA guidance. Regulations change; check the current text at eCFR and the ACS. Checked against current sources 2026-11-13.