Free sim
Engine Run-Up
The run-up is the one systems check you fly every single flight — and the checklist only tells you what to do, not what the engine is telling you back. Start it, run it up, and read the needles: mag drops, carb-heat response, oil, suction, and the ammeter. Then try the fault scenarios and diagnose them from the evidence, the way a mechanic would.
Engine secure. Electrical bus unpowered; oil pressure and ammeter are not indicating. Current step: Start and stabilize.
Trainer limits: max 175 RPM drop on either magneto; max 50 RPM difference between the two drops. Your airplane's AFM/POH governs.
Sources for the magneto numbers
Where these numbers come from. Lycoming Service Instruction No. 1132B, “Magneto Drop-off”, revised 18 June 2010, page 2: drop-off must not exceed 175 RPM and must not exceed 50 RPM between magnetos. It covers all Lycoming opposed-series aircraft engines with magnetos, which is the engine class this trainer represents. These are the engine manufacturer's figures.
There is no FAA number. The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C, 2023) p. 7-15 says only “The permissible decrease is listed in the AFM or POH.” The Airplane Flying Handbook (FAA-H-8083-3C) ch. 2 p. 2-21 asks only that magneto operation be “within limits”. Published limits also vary by installation — S.I. 1132B itself notes 100 RPM for the O-290-D2 and 200 RPM for helicopter installations.
Two disclosures. This trainer checks at 1,700 RPM, an airframe-checklist convention; Lycoming publishes the 175-RPM figure at approximately 1,800 RPM. And the 20-RPM floor this sim uses for “no drop” is a sim convention — no source publishes a minimum acceptable drop.
Why oil pressure and the ammeter go blank with the master off
This trainer models the oil pressure indication as electrically powered, so it reads nothing with the master switch off. That matches FAA SAIB CE-19-01 R1 (6 December 2022), which states that on the Cessna 172R/S “the oil pressure gauge/indicator is driven by a separate dedicated pressure transducer.” Other airplanes — including many older cluster-gauge trainers — use a direct-reading Bourdon-tube gauge plumbed to an oil line, which needs no ship power (FAA-H-8083-32B, ch. 6, pp. 6-8 to 6-9). We do not model yours; check your AFM/POH.
The engine is unaffected either way: the magnetos need no ship power at all — “A magneto uses a permanent magnet to generate an electrical current completely independent of the aircraft’s electrical system” (FAA-H-8083-25C, 2023, p. 7-15). An unpowered gauge is shown flagged UNPWR rather than at zero, because a zero from a dead instrument is not evidence of anything, and this sim will not grade one.
Active: Healthy baseline
Engine is secure.
- 1 Start and stabilize
- 2 Set 1,700 RPM
- 3 Check RIGHT
- 4 Return to BOTH
- 5 Check LEFT
- 6 Return to BOTH
- 7 Apply carburetor heat
- 8 Carb heat COLD
- 9 Verify engine instruments
- 10 Return to idle
- 11 Check ignition grounding
- 12 Run-up complete
No qualified observations yet. Operate the panel to begin.
Findings appear only after qualified instrument observations — the hidden scenario is never used as a shortcut.
Cause and evidence: Healthy baseline
- What is happening
- The engine and supporting systems are responding normally throughout the run-up.
- Why
- Both ignition channels contribute evenly, carb heat changes the intake-air path, engine-driven oil and vacuum sources rise with RPM, and the alternator supports the selected load.
- Evidence to expect
- Near 1,700 RPM, each single-magneto selection produces a modest and similar drop, BOTH restores RPM, carb heat produces a temporary drop, and the oil, suction, and ammeter indications remain in profile.
- Takeaway
- Use this healthy pattern as the comparison baseline. Drop size, side-to-side symmetry, and recovery are more useful together than any single reading.
Two habits this sim is built to teach: first, a magneto check is a comparison, not a number — drop size, side-to-side symmetry, and the recovery when you return to BOTH matter together. Second, “no drop” is not a pass — PHAK FAA-H-8083-25C (2023) p. 7-16 says “no drop” in RPM is not normal and that the aircraft should not be flown. It points to an ignition-control or grounding discrepancy: the switch may not have actually removed an ignition source. Instrument markings and fault magnitudes here are illustrative trainer values, not type-specific limits — fly your aircraft by its own POH.
The comparison now has a number attached to it. Lycoming Service Instruction No. 1132B, “Magneto Drop-off”, revised 18 June 2010, page 2, puts both halves in one sentence: the drop must not exceed 175 RPM, and must not exceed 50 RPM between magnetos. Those are the engine manufacturer’s figures for Lycoming opposed-series engines, not FAA limits and not approved limits for your airplane — the FAA handbooks publish no number at all and refer you to the AFM or POH. The sim enforces both halves, and tells you when it could not evaluate one rather than passing you on half the evidence.
Carb ice is not only a cold-weather problem, and published sources draw the line in different places — on temperature, and on how dry the air has to be before you can stop worrying about it. PHAK FAA-H-8083-25C (2023) p. 7-9 carries two figures: icing is most likely when temperatures are below 70 °F and relative humidity is above 80 %, and it can occur even at outside air temperatures as high as 100 °F with humidity as low as 50 %. FAA AC 20-113 (22 October 1981), paragraph 5.c, states that same 50 % as a floor across a wider band: fuel-vaporization icing may occur from 32 °F to as high as 100 °F with a relative humidity of 50 percent or above. NTSB Safety Alert SA-029 (Dec 2013, rev. Dec 2015) reports serious carburetor icing in temperatures as high as 90 °F or humidity as low as 35 %, and UK CAA Safety Sense Leaflet 14 (June 2023) puts serious icing at descent power with humidity as low as 30 %. They differ by power setting and severity threshold. We show the disagreement rather than pick a number.
The ignition grounding check is in here too, at low power — though the published figures differ on how low. The Airplane Flying Handbook (FAA-H-8083-3C) p. 2-23 says “at idle rpm”, while the AMT Handbook — Powerplant (FAA-H-8083-32B) gives two of its own: p. 4-31 says the check is usually made at 700 RPM, and p. 10-26 places it during warm-up at approximately 1,000 RPM. Move the switch briefly to OFF and the engine should begin to cut out; FAA-H-8083-32B’s pass criterion is that it cuts out completely. If it does not, a P-lead is not grounding, the magnetos are live whatever the switch says, and per PHAK p. 7-16 the mixture is the only thing that will stop the engine.
Training simulator only — not an aircraft checklist or a substitute for the POH. Engine and control sounds are CC0 recordings; see the audio credits.
Drilling for the checkride?
Ignition systems, carb ice, and the why behind every run-up item are covered in our ACS-organized Private Pilot Quick-Review Study Guide — the systems answers examiners actually ask for.