Instrument rating · ACS IR.II.A · lesson pack

Aircraft Systems for IFR

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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.

1 · Know these cold

•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))

2 · The lesson

Ice protection

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

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))

Want it all on one page, with scenarios? Read the full lesson.

3 · Say it out loud

Answer each one out loud, then check yourself and mark how it went.

Remember Recall it
“What is the difference between anti-ice and deice?”
Understand Explain why
“Why can an autopilot be dangerous in icing?”
Apply Use it on a flight
“In cloud at 6,000 feet you see ice forming on the windshield frame. What do you do?”

4 · 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.

5 · Quick check

Answer, then reveal. Flag anything you want to see again.

1. What two things does structural icing need?
2. Where does it say whether your airplane is approved for known icing?
3. Anti-ice or deice: pneumatic boots?
4. What happens to the airspeed indicator with a blocked pitot tube and an open drain?
5. Name two ways to disconnect your autopilot.
Scenario6. Picking up ice in cloud. First actions?

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Connect it

One situation that runs across this lesson and its neighbors in the same ACS area. Decide first, then check.

Connect it · Preflight Procedures

In cloud near freezing, airspeed starts falling toward zero while attitude, power and altitude are unchanged. Later the attitude indicator slowly tilts while the turn coordinator shows wings level.

Diagnose both and connect them to the checks before flight. Decide, then see the worked answer

Airspeed falling toward zero with nothing else changing points to a blocked pitot inlet, likely ice, with the drain hole still open: the pressure in the line bleeds away, so the reading falls. (If the inlet and the drain are both blocked, the indicator acts like an altimeter instead, rising in a climb and falling in a descent.) Pitot heat should already be on in visible moisture near freezing. Turn it on, but don't count on the reading coming back: fly a known attitude and power setting, treat the airspeed as unreliable, tell ATC, and get out of the icing. Diagnose the attitude indicator by its power source. Check the suction gauge: low suction means a vacuum failure, so distrust both vacuum gyros, the attitude and heading indicators in a typical trainer, and cover them. Fly partial panel on the turn coordinator, the magnetic compass, and the altimeter, VSI and airspeed. Which instruments run on vacuum and which on electric power is airplane-specific, so know yours. Tell ATC and request a clearance that gets you out: vectors or a route to VFR conditions or the nearest suitable airport. Declare an emergency under 91.3 only if you need to deviate from a clearance. Both trace back to the instrument flight deck check, done in phases. Before start: instruments set and checked. After start: give the gyros about 5 minutes to spin up, check suction in the normal range (typically 4.5 to 5.5 inches of mercury), and check the pitot heat. While taxiing: set the heading indicator to the compass, and check the turn coordinator deflects in turns and the attitude indicator stays steady.

IFH (FAA-H-8083-15B), Flight Instruments; 14 CFR 91.3

Brings together: Aircraft Systems Related to Instrument Flight Rules (IFR) Operations · Aircraft Flight Instruments and Navigation Equipment · Instrument Flight Deck Check

Teaching this? The instructor lesson plan →

Study aid, not FAA guidance. Sources: AC 91-74B; Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); Instrument Flying Handbook (FAA-H-8083-15B); Advanced Avionics Handbook (FAA-H-8083-6); Instrument Rating ACS (FAA-S-ACS-8C). Checked against current sources 2026-11-13.