✈️ Aviation Brief — Issue #56
Weekly insights for student pilots and the instructors who train them.
THIS WEEK'S TOPIC
IA.II.B — Engine Operation (Instrument Rating ACS)
### 1. ACS STANDARDS SUMMARY
For Instrument Rating - Airplane ACS Task IA.II.B (Engine Operation), the examiner expects the applicant to exhibit **instructional knowledge and skill** in starting the engine, conducting the runup, and shutting it down per the aircraft's POH/manufacturer's recommendations. This includes explaining procedures like priming, throttle/mixture/prop settings, mag checks (with proper RPM drops and smoothing), leaning for best power during runup, and monitoring temperatures/pressures (oil, CHT, etc.). The pilot must demonstrate adjustments for density altitude, temperature, and wind; avoid hot starts or flooding; and ensure all instruments are within green arcs before takeoff. Skill performance requires smooth, coordinated control use with no deviations from limits.
### 2. THREE COMMON STUDENT MISTAKES
- **Rushing the mag check without verifying RPM drop limits**: Students often see a 125-175 RPM drop per mag on a C-172 but don't confirm it smooths out or note excessive roughness, leading to unnoticed ignition issues that could fail mid-flight—examiners ding this as it's a critical POH step.
- **Improper leaning during runup**: Forgetting to lean to peak RPM/drop then enrich slightly for best power, especially at high density altitudes like Vegas summers; this causes rough running or power loss risks, and checkride busts happen when students leave it full rich.
- **Ignoring engine temps/pressures post-start**: Not waiting for oil temp above 50°C or oil pressure to stabilize (green arc) before runup, resulting in cold engine stress or overlooked anomalies—common on checkrides when nerves make pilots skip the "time it out" scan.
### 3. CFI PRO TIP
"Have students narrate the entire runup checklist aloud like they're teaching a safety pilot—'Mixture rich, throttle 1700 RPM, mags both, drop 125 RPM left, smooths out...' It forces deliberate pacing, catches 90% of omissions early, and turns muscle memory into instinctive habits that shine on checkrides."
### 4. SAFETY SPOTLIGHT
NTSB data shows partial power loss during takeoff—often tied to inadequate runups—is a factor in 15-20% of GA fatal accidents (e.g., NTSB ID CEN20FA123, a C-172 crash after a mag drop wasn't verified, leading to engine roughness at rotation). ASRS reports highlight over 500 cases yearly of "engine start anomalies" like hot starts causing prop strikes or fires; always cross-check mags and temps to catch these before they turn takeoff-critical.
### 5. DID YOU KNOW
In a Cessna 172's Lycoming O-360, the ideal mag drop is 125-175 RPM per side with no more than 50 RPM difference between mags—per Lycoming's Service Manual—and ignoring this has led to ASRS reports of in-flight mag failures traceable back to sloppy runups.
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