16.engine-failure-cruise. Engine Failure During Cruise Flight
An engine failure during cruise flight is generally less critical than one occurring shortly after takeoff because the airplane is at altitude with time to think, troubleshoot, and plan. The pilot's first job is to fly the airplane: establish best-glide airspeed, then turn toward a suitable landing area before doing anything else. Time spent troubleshooting at altitude is time well spent only if the airplane is already trimmed for glide and pointed somewhere survivable.
Immediate Actions
When the engine quits or begins running roughly enough that a complete failure is likely, the pilot should accomplish the following memory items, in order:
- Pitch for best glide. Establish the airplane's published best-glide airspeed (commonly 65-75 KIAS in light singles). Trim to hold it hands-off. Best glide gives the maximum distance per foot of altitude lost — typically a glide ratio of about 9:1 in trainers, meaning roughly 1.5 nm of glide per 1,000 ft AGL in still air.
- Pick a landing site. Scan within glide range. Favor into-wind, level, firm surfaces: paved or hard-surface roads, runways, plowed fields, pastures. Avoid populated areas, soft sand, tall crops, water, and surfaces with wires or fences.
- Turn toward the field. Trade altitude for position only after best glide is established. Do not stretch the glide.
Troubleshooting Flow
Once the airplane is configured and the field selected, attempt a restart using the manufacturer's checklist. A typical flow in a carbureted single is:
- Fuel selector — switch tanks (most common cause of cruise engine failure is fuel mismanagement).
- Mixture — RICH (or adjust for altitude).
- Carburetor heat — ON.
- Primer — IN and locked.
- Magnetos — check L, R, then BOTH; try START if propeller has stopped.
- Master/alternator — verify ON.
- Auxiliary fuel pump — ON (in fuel-injected airplanes, follow the engine-driven-pump-failure or hot-start procedure as applicable).
If the engine restarts, climb cautiously, monitor engine instruments, and divert to the nearest suitable airport. Do not assume the problem is solved.
Communication and Squawk
If time and altitude permit after the airplane is under control:
- Communicate on 121.5 MHz or the current ATC frequency. Use the word MAYDAY three times, state callsign, position, altitude, problem, intentions, and souls on board with fuel remaining.
- Squawk 7700 on the transponder.
- ELT — verify ON if a forced landing is imminent.
ATC can provide vectors to the nearest airport, weather, and alert search-and-rescue. However, do not let radio work distract from flying the airplane and managing the glide.
Glide Planning
Know your airplane's glide performance from the POH. As a rule of thumb, in a typical trainer at best glide:
- Glide distance (nm) ≈ altitude AGL (ft) × glide ratio ÷ 6076.
- A 9:1 ratio at 5,000 ft AGL yields roughly 7.4 nm of still-air glide.
- Headwinds shrink that distance significantly; tailwinds extend it. Always pick a field upwind or crosswind of your position when possible.
A banked turn costs altitude rapidly. A 180° turn back toward a field behind you can consume 800-1,000 ft. Plan ahead so reversal turns are rarely needed.
Forced Landing Configuration
When committed to a forced landing:
- Brief passengers: seats upright, belts and shoulder harnesses tight, doors unlatched on short final to prevent jamming.
- Plan a high key point roughly over the intended touchdown at 1,500-2,000 ft AGL, a low key abeam the touchdown at about 1,000 ft AGL, and base/final flown like a power-off 180.
- Do not extend full flaps until landing is assured. Once assured, full flaps slow the touchdown.
- Fuel selector OFF, mixture ICO, mags OFF, master OFF just before touchdown to reduce fire risk; leave the master on long enough to deploy flaps if electric.
- Touch down at the slowest controllable speed, wings level, in a slightly nose-high attitude.
Common Errors
- Failing to establish and trim for best glide before troubleshooting.
- Stretching the glide — pitching up below best glide guarantees a stall and a shorter glide.
- Picking a field too far away or downwind.
- Skipping the restart flow because the pilot assumed the cause.
- Forgetting to unlatch doors before touchdown.
The key takeaway from the Airplane Flying Handbook is that altitude is time, and time is options. A pilot who aviates first, navigates to a field second, and communicates third will turn most cruise engine failures into a survivable, often uneventful, off-airport landing.