In-Flight Engine Restart: Critical Guidance for Crews

An analysis of over 1,000 pilot self-reports found that approximately 80% of respondents who experienced a complete engine power loss landed with a reusable aircraft and no physical harm to occupants. When partial power remained available, the odds of a safe outcome improved to roughly 30:1. These figures underscore a consistent theme in aviation safety data: effective training, procedural discipline, and structured decision-making during engine anomalies are the primary determinants of outcome. FlySafe analysis shows that understanding engine restart procedures — and, equally important, understanding when not to attempt a restart — remains a foundational competency for all flight crews.

The Decision Framework: Restart or Secure

The first and most consequential decision following an engine anomaly is whether to attempt a restart at all. This determination is not a single binary choice but a structured assessment informed by aircraft type, phase of flight, failure indications, and environmental conditions.

According to the Boeing 737NG Abnormal Procedures Handbook, the guidance under "ENGINE FAILURE/SHUTDOWN" directs flight crews to "accomplish an engine shutdown only when flight conditions permit" and to "plan to land at the nearest suitable airport." The emphasis in this language is deliberate: the default posture is to secure the engine and plan for a single-engine approach, not to pursue a restart as a first-order priority.

For larger multi-engine transport category aircraft, the loss of a single engine en route is managed through well-established procedures. On the Boeing 747, for example, the loss of an engine without restart capability en route has historically not been classified as a serious emergency. The decision to divert or continue to destination has typically rested with the captain, based on factors including remaining fuel, weather at available alternates, and aircraft performance margins.

The FAA's Airplane Flying Handbook (FAA-H-8083-3C) provides unambiguous guidance for one critical scenario: if an engine fire has been extinguished, "no attempt should be made to restart the engine." This prohibition reflects the risk that a restart could re-introduce fuel or oil flow to a compromised area, reigniting a fire in conditions where suppression options may already be depleted.

Memory Items and Restart Sequences

Across aircraft types, engine restart procedures share common structural elements while differing in specific steps. The critical point is that these procedures must be committed to memory, practiced regularly, and executed with precision under stress.

For general aviation aircraft, the restart sequence is typically straightforward but demands disciplined adherence. The Cessna 172 emergency procedures specify the following restart checklist: fuel selector to BOTH, mixture to RICH, throttle to FULL OPEN, carburetor heat ON, ignition to BOTH, master switch ON, and primer IN and LOCKED. If the restart attempt fails, the procedure directs the pilot to clear the engine every 30 seconds while preparing for a power-off approach. A minimum altitude of 500 feet AGL is stipulated for restart attempts — below this threshold, the crew's attention and available time must be devoted entirely to landing site selection and approach configuration.

As noted in Aviation Safety Magazine, memory items for an engine restart in piston-powered aircraft generally include checking the magnetos, power settings, carburetor heat, fuel selector, fuel pump, and other controls. The ordering of these items varies by aircraft manufacturer and type, but the underlying logic is consistent: verify fuel supply, confirm ignition capability, and establish conditions favorable for combustion.

For turbine-powered aircraft, the restart procedure is more complex and typically involves different modes depending on altitude and airspeed. The concept of a "windmill restart" — using ram air to spin the engine to sufficient RPM for ignition — is standard at higher altitudes and airspeeds where the airflow through the engine is adequate. At lower altitudes or airspeeds, a starter-assisted restart may be required, drawing on the aircraft's electrical or pneumatic systems.

All-Engines-Out: A Distinct Category of Urgency

The total loss of thrust from all engines represents a qualitatively different scenario from a single-engine failure. The Transport Canada Civil Aviation guidance document TCCA-002 provides a regulatory framework for how aircraft manufacturers should address this contingency in the Aircraft Flight Manual (AFM).

The guidance specifies that applicants for type certification should identify procedures for restarting engines during all-engines-out conditions, including "an immediate restart procedure." This reflects the understanding that time is the most constrained resource in a total power loss scenario; the crew must have a rapid-access procedure that can be initiated from memory without reference to lengthy checklist sequences.

Where start cartridges are proposed as part of the restart system, the TCCA guidance stipulates that "the applicant should provide the capability for at least two start attempts of each engine." This redundancy requirement acknowledges that a single restart attempt may not succeed due to transient conditions, improper sequencing, or environmental factors, and that the crew must retain options.

The guidance further emphasizes flight deck design considerations. The crew must have clear awareness of "an engine flameout or sub-idle engine" through unambiguous flight deck indications. Equally important, the crew must receive confirmation that "the start is clearly progressing normally" and that "the engine has reached idle or selected power setting." Ambiguity in engine status during a restart attempt can lead to premature abandonment of a successful start or, conversely, to continued reliance on an engine that has not actually achieved stable operation.

A human factors evaluation is also recommended to determine whether visual cues alone are sufficient "to assure the flightcrew will initiate the correct procedures within the in-flight engine restart envelope." This speaks to the broader challenge of designing restart procedures that are executable under the high-stress, time-compressed conditions of a total power loss event.

Engine-Specific Considerations and Common Failure Modes

Not all engine failures are created equal, and the likelihood of a successful restart is heavily influenced by the root cause of the initial power loss. Understanding the most common failure modes for a given engine type informs both the decision to attempt a restart and the technique employed.

For the Pratt & Whitney JT9D series, as noted by experienced operators, the most common cause of an in-flight shutdown is "poor technique on the part of the pilot." Specific guidance for this engine type includes lowering the nose before retarding the thrust levers and avoiding abrupt throttle movements, particularly above FL370 where the air is thin and the engine's surge margins are reduced. The recommendation to "take a few seconds" when reducing thrust levers reflects the aerodynamic and thermodynamic realities of high-altitude engine operation, where rapid power changes can induce compressor stalls or flameouts.

This insight carries broader applicability. Many in-flight engine shutdowns in turbine-powered aircraft result from fuel management errors, inadvertent thrust lever movements, or environmental ingestion events (such as volcanic ash or severe precipitation) rather than from catastrophic mechanical failure. In these scenarios, the prospects for a successful restart are generally favorable, provided the crew follows the correct sequence and allows adequate time for engine spool-up.

Conversely, engine shutdowns precipitated by mechanical failure — such as bearing seizure, turbine blade liberation, or uncontained rotor burst — present a fundamentally different risk profile. As documented by the FAA's Propulsion and Fuel Systems Program, "when engine parts break due to abnormalities in the metal, fragments can escape the engine case and impact other parts of the aircraft." In such cases, a restart attempt is not only unlikely to succeed but may introduce additional hazards, including fire risk from fuel flowing into a compromised engine section.

The Role of Training and Startle Response Management

The technical knowledge of restart procedures is necessary but not sufficient. The human factors dimension — specifically, the management of startle response and the maintenance of cognitive function under acute stress — is equally determinative of outcomes.

Research cited by the FAA's General Aviation Joint Steering Committee has shown that "startle responses during unexpected situations such as power-plant failure during takeoff or initial climb have contributed to loss of control of aircraft." The physiological startle response — characterized by elevated heart rate, narrowed attention, and degraded fine motor control — directly impairs the pilot's ability to execute the precise, sequenced actions required for an engine restart or secure procedure.

The primary mitigation for startle response is pre-briefing. By including "an appropriate plan of action in a departure briefing for a power-plant failure during takeoff or initial climb," crews can establish a cognitive framework that reduces the novelty of the event and channels the stress response into pre-rehearsed actions. This principle applies not only to takeoff and initial climb but to all phases of flight. Crews who have mentally rehearsed the engine failure and restart scenario for their current conditions — altitude, weather, proximity to suitable airports — are significantly better positioned to execute effectively when the event occurs.

The FAA's Emergency Procedures Training guidance reinforces this through its emphasis on scenario-based training, noting that the General Aviation Joint Steering Committee "believes that scenario-based training in emergency procedures will be effective in reducing these kinds of mishaps." The document highlights a particularly important asymmetry in multi-engine operations: while an engine failure represents a 50% loss of available power, "it can result in as much as an 80% loss of performance." This non-linear relationship between power loss and performance degradation means that crews must be trained to recognize and manage the full magnitude of the performance deficit, not merely the arithmetic reduction in available thrust.

For multi-engine aircraft, the best single-engine climb speed (Vyse) becomes the target airspeed following an engine failure. Regarding single-engine go-arounds in light twins, the FAA guidance is direct: they "often don't go well and they should be avoided if possible." This has direct implications for the restart decision — if a restart attempt is consuming time and attention that would otherwise be devoted to configuring the aircraft for a single-engine approach, the attempt may itself become a hazard.

Frequency of Events and Statistical Context

Survey data provides useful context for understanding the frequency of engine power loss events. According to a survey of over 1,000 pilots, the average logged flight hours between loss-of-power events that caused an unwanted landing was approximately 2,000 hours among the subset of pilots who self-reported such events. While this figure is subject to reporting bias and reflects primarily general aviation operations, it establishes that engine power loss, while uncommon in any individual flight, is a realistic contingency across a pilot's career.

Airspace status: The relevance of engine restart proficiency extends beyond individual crew competency to systemic operational planning. Airlines operating in regions with extended overwater segments, remote terrain, or limited diversion options face heightened exposure to scenarios where an engine restart capability — or the lack thereof — may determine the outcome. FlySafe analysis shows that route-specific risk assessment should account for the availability of suitable diversion airports and the performance implications of single-engine or no-engine operation over challenging terrain.

Key Takeaways for Flight Crews

Recommendation: The following principles, drawn from publicly available regulatory guidance and operational data, represent the core framework for engine restart decision-making:

1. Secure first, restart second. The priority following an engine anomaly is to maintain aircraft control, configure for single-engine flight, and establish a plan for landing at the nearest suitable airport. A restart attempt is a secondary consideration, undertaken only when conditions permit and the failure mode does not contraindicate it.

2. Know the failure mode. A fuel-related or pilot-induced shutdown presents favorable conditions for restart. A mechanical failure with abnormal vibration, fire indication, or evidence of structural damage does not. If the cause is unknown, the conservative approach is to treat it as potentially mechanical.

3. Respect altitude and time constraints. Restart attempts consume altitude and attention. Below minimum altitudes specified in the aircraft's emergency procedures, the crew's focus must shift entirely to landing.

4. Pre-brief and rehearse. The startle response is real and measurable. Pre-departure briefings that explicitly address the engine failure scenario for the current phase of flight are the most effective mitigation.

5. Train to the standard, not above it. Scenario-based training in engine failure and restart procedures, conducted regularly, builds the procedural fluency and stress tolerance that enable effective performance during actual events.

Based on publicly available NOTAMs, regulatory guidance, and operational data, engine restart procedures are well-established across aircraft types and well-supported by manufacturer and regulatory documentation. The challenge lies not in the availability of guidance but in the consistent application of that guidance under the time pressure and cognitive load of an actual engine anomaly.

FlySafe continues to monitor developments in engine reliability, restart certification requirements, and crew training standards as part of its ongoing aviation risk intelligence service. Flight crews and operators seeking to evaluate route-specific risk factors associated with engine performance contingencies are encouraged to consult FlySafe's analytical resources.

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Analysis based on publicly available data only. FlySafe Research does not possess, access, or utilize any classified or non-public information. All referenced documents are publicly available through their respective regulatory authorities.