IFR Emergencies & System Failures

Pitot-Static System Failures

The pitot-static system provides ram air pressure and static (ambient) air pressure to three instruments: the airspeed indicator, altimeter, and vertical speed indicator. Understanding what happens when components of this system fail is critical for instrument pilots and one of the most tested topics on the oral exam.

Static Port Blockage

When the static port becomes blocked (ice, debris, insects), the instruments react as follows:

• Altimeter: Freezes at the altitude where the blockage occurred — will not change regardless of actual altitude changes
• VSI: Zeros out and remains at zero — no indication of climb or descent
• ASI: Becomes unreliable at altitudes different from where the blockage occurred. If you climb above the blockage altitude, the ASI reads lower than actual (trapped static pressure is higher than ambient). If you descend below the blockage altitude, the ASI reads higher than actual (trapped static pressure is lower than ambient).

Pitot Tube Blockage

The pitot tube supplies ram air pressure to the airspeed indicator only. The altimeter and VSI are unaffected by pitot blockage.

• Ram air inlet blocked, drain hole open: ASI drops to zero as ram air pressure bleeds out through the drain hole
• Ram air inlet AND drain hole blocked: ASI freezes at current indication. If you climb, ASI reads higher than actual (trapped ram air pressure stays constant while static pressure decreases). If you descend, ASI reads lower than actual. The ASI effectively becomes an altimeter — reads like an altimeter, increasing with altitude gain.

Alternate Static Source

Most aircraft have an alternate static source that draws air from inside the cockpit. Because cockpit pressure is slightly lower than outside ambient pressure (due to aerodynamic effects), using the alternate static source produces predictable errors:

• ASI: Reads slightly faster than actual (lower static pressure increases the differential)
• Altimeter: Reads slightly higher than actual altitude
• VSI: Shows a momentary indication of a climb when first activated, then settles

Gyroscopic Instrument Failures

Gyroscopic instruments in most training aircraft are powered by two different sources, which means different failures affect different instruments:

Vacuum Pump Failure

When the vacuum pump fails, both the AI and HI become unreliable. This is insidious because the instruments do not immediately show obvious errors — they slowly drift as the gyros spin down. Watch for:

• Low suction gauge reading (below the green arc)
• AI and HI slowly disagreeing with other instruments
• AI showing a slight bank when the turn coordinator shows wings level

Electrical Failure Effects on Instruments

An electrical failure takes out the turn coordinator. In this case, you still have the vacuum-driven AI and HI — but you lose the ability to cross-check turn rate. The inclinometer (ball) is mechanical and continues to function.

Partial Panel Flying Techniques

When flying partial panel (no AI, no HI), use the remaining instruments:

• Turn coordinator: Use for bank control — wings level = straight flight
• Magnetic compass: Use for heading reference (with acceleration/turning errors)
• Airspeed indicator: Use for pitch reference — if airspeed is stable, pitch is stable
• Altimeter and VSI: Cross-check for pitch confirmation

Unusual Attitudes

An unusual attitude is any aircraft attitude not normally required for instrument flight. Recognition and recovery must be immediate:

Nose-High Unusual Attitude

Indications: Decreasing airspeed, increasing altitude, positive VSI.

Recovery:

1. Add power (prevent stall)
2. Lower the nose (reduce pitch attitude)
3. Level the wings (using turn coordinator if partial panel)

Nose-Low Unusual Attitude

Indications: Increasing airspeed, decreasing altitude, negative VSI.

Recovery:

1. Reduce power (prevent overspeed)
2. Level the wings (stop the descent from increasing)
3. Raise the nose (gently — do not pull excessive G-loads)

G1000 Reversionary Mode

The Garmin G1000 integrated flight deck has a built-in backup: reversionary mode. If the PFD (Primary Flight Display) fails, the MFD (Multi-Function Display) can display PFD data.

Automatic Reversion

If the G1000 detects a PFD failure, the MFD automatically enters reversionary mode, displaying critical flight instruments on the MFD screen. The display splits to show:

• Attitude indicator, airspeed tape, altitude tape, and HSI on the MFD
• Engine instruments compressed to the top of the display
• Map display reduced or removed

Manual Reversion

The pilot can also trigger reversionary mode manually by pressing the red DISPLAY BACKUP button between the two screens. This is useful if the PFD is displaying erratic information but has not fully failed.

Electrical Failure Hierarchy

Understanding the aircraft electrical system helps you manage failures systematically:

Alternator Failure

If the alternator fails, the battery becomes the sole power source. You have limited time (typically 30-60 minutes depending on electrical load) before the battery is depleted.

1. Shed non-essential loads: Turn off autopilot, unnecessary lighting, second radio, second nav source
2. Advise ATC: Declare the situation, request priority handling or vectors to the nearest suitable airport
3. Plan for total electrical failure: Brief the non-GPS approach at your destination, note compass headings

Essential Bus

Most aircraft have an essential bus (or emergency bus) that receives power from the battery even if the main bus fails. Critical instruments on the essential bus typically include:

• One COM radio
• One NAV radio
• Transponder
• Engine instruments
• Basic flight instruments

Load Shedding Priority

When managing an electrical emergency, shed loads in this general order (least critical first):

1. Cabin lighting, entertainment
2. Autopilot
3. Second COM/NAV radio
4. GPS (if you have a VOR/LOC approach available)
5. Transponder (keep as long as possible for radar identification)

Emergency Transponder Codes

Three transponder codes are reserved for emergency situations. Know these cold:

Generic Instrument Taxi Check

Before every IFR flight, perform this systematic check of all flight instruments during taxi. This is your last chance to catch a failed instrument on the ground:

ATC Audio Practice

Listen to each ATC audio clip in sequence. Practice your readback before listening to the correct version:

1. Briefing:
2. Pilot Initial Call:
3. ATC Response:
4. ATC Clearance:
5. Pilot Readback:
6. ATC Clearance (Repeat):
7. Pilot Readback 2:
8. ATC Final Confirmation:

Scenario 1: PFD Failure — MFD Reversionary Mode

During cruise at 5,000 ft en route to Hartford, the instructor will simulate a PFD failure. The MFD should automatically enter reversionary mode.

Your Actions

1. Recognize the failure: PFD screen goes blank or displays error flags
2. Confirm reversionary mode: Verify the MFD is displaying PFD flight data (attitude, airspeed, altitude, HSI)
3. If automatic reversion did not activate: Press the red DISPLAY BACKUP button
4. Adjust your scan: Your primary instruments are now on the right screen — adapt your cross-check
5. Advise ATC: Report the equipment failure and request priority handling if needed
6. Continue the flight: Maintain heading, altitude, and airspeed using the MFD display

Scenario 2: ADC Failure — Compass and Backup Attitude

After the PFD is restored, the instructor will fail the Air Data Computer (ADC). This removes computed airspeed, altitude, and vertical speed from the G1000 displays. You must transition to backup instruments.

Available Instruments

• Standby attitude indicator: Your primary pitch and bank reference
• Magnetic compass: Your only heading reference (with acceleration and turning errors)
• Standby airspeed indicator: Mechanical ASI connected to pitot-static system
• Standby altimeter: Mechanical altimeter

Flying Technique

1. Set a known power setting for the desired airspeed (e.g., 2300 RPM for 100 KIAS in cruise)
2. Use the standby attitude indicator for pitch and bank
3. Make small heading corrections — the magnetic compass has significant errors during turns and acceleration
4. For heading changes: use timed turns with the clock and turn coordinator (standard rate = 3°/second)

Scenario 3: Non-GPS Approach

With degraded navigation capability, you will fly a LOC or VOR approach at the destination airport without GPS guidance. This simulates a real-world scenario where GPS has been lost or is unreliable.

Approach Execution

1. Brief the approach: Identify the final approach course, FAF, MDA, missed approach point, and missed approach procedure
2. Tune and identify the navaid: Verify the Morse code identifier — do not rely on the frequency alone
3. Fly the procedure turn or course reversal: Establish on the final approach course inbound
4. Time from the FAF: Start timing at the FAF — your backup missed approach point is time-based
5. Descend to MDA: Use Dive & Drive — descend promptly after the FAF
6. Execute missed approach if needed: At the MAP without the runway environment in sight, go missed

Performance Standards

Note that partial panel tolerances are wider than normal instrument flight. The ACS recognizes that flying without primary instruments is significantly more challenging. However, you must still maintain positive aircraft control at all times.

Key Takeaways

1. Static port blockage freezes altimeter and zeros VSI. The ASI becomes unreliable at altitudes different from where the blockage occurred — it effectively acts as an altimeter.
2. Pitot tube blockage (both ports) makes the ASI act like an altimeter. ASI increases with altitude gain, decreases with altitude loss. Only ASI is affected — altimeter and VSI remain accurate.
3. Alternate static source reads fast and high. ASI reads slightly faster, altimeter reads slightly higher, VSI shows momentary climb — all because cockpit static pressure is lower than ambient.
4. Vacuum pump failure kills the AI and HI. The failure is insidious — instruments drift slowly. Cross-check the turn coordinator (electrically powered) against the AI. If they disagree, trust the turn coordinator.
5. Partial panel = turn coordinator + compass + airspeed. Use timed turns for heading changes (standard rate = 3°/sec). Remember UNOS for compass turning errors.
6. G1000 reversionary mode is your backup. PFD fails, MFD displays flight instruments. Know the DISPLAY BACKUP button location. Practice reading the compressed display.
7. Emergency squawk codes: 7700, 7600, 7500. Emergency, lost comms, hijack. Never accidentally squawk 7500.

Oral Exam Self-Test

1. What three instruments are connected to the pitot-static system? Which use static pressure only, and which use both pitot and static?
2. If the static port becomes blocked, what happens to the altimeter, VSI, and ASI?
3. If the pitot tube is completely blocked (ram air inlet and drain hole), how does the ASI behave during a climb? During a descent?
4. What are the effects of using the alternate static source on ASI, altimeter, and VSI?
5. Which gyroscopic instruments are vacuum-powered? Which are electrically powered?
6. How do you recognize a vacuum pump failure? Why is it considered the most dangerous instrument failure?
7. Describe the recovery procedure for a nose-high unusual attitude. Why is adding power the first step?
8. Describe the recovery procedure for a nose-low unusual attitude. Why do you level the wings before raising the nose?
9. What is G1000 reversionary mode? How is it activated automatically? Manually?
10. What is the order of load shedding during an electrical failure? What stays on the essential bus?
11. What do transponder codes 7700, 7600, and 7500 mean? When do you use each?
12. Walk through the instrument taxi check — what should each instrument show before takeoff?

Pilot Preparation for Lesson 10

Lesson 10 is your checkride preparation and comprehensive IFR oral exam review — covering all material from Lessons 1 through 9 (KTTN → KTAN).

Preparation

1. Review all lesson notes: Go through key takeaways from Lessons 1-9
2. Practice oral exam questions: Answer every oral exam question from every lesson review page — out loud, as if speaking to an examiner
3. Review ACS: Read the Instrument Rating ACS (FAA-S-8081-66C) — areas of operation, tasks, and standards
4. Weather review: Be prepared to discuss weather minimums, alternate requirements, and go/no-go decision-making
5. Approach plates: Be ready to brief any approach type — ILS, LOC, VOR, RNAV/GPS, LPV

Key Topics to Master

• IFR flight planning: weather, NOTAMs, fuel requirements, alternate airports
• Airspace, ATC clearances, and lost communications procedures
• All approach types: precision, non-precision, RNAV/GPS
• Holding patterns: entries, timing, wind correction
• System failures: pitot-static, gyroscopic, electrical
• Weather theory: icing, thunderstorms, fog, frontal systems
• Regulations: 14 CFR 91.167 through 91.185

Resources

• Instrument Rating Files — Partial panel procedures, emergency checklist, system failure decision trees
• Instrument Flying Handbook (FAA-H-8083-15B)
• Instrument Rating ACS (FAA-S-8081-66C)