A Pilot's First 60 Seconds: What Happens When an Engine Fails

 An engine failure doesn't necessarily translate to a catastrophic accident. From the physics of an unpowered glide to the split-second decisions pilots make, this article will help you understand how aircraft are safely landed when thrust dissipates.

As the crimson-coloured setting sun disappeared below the horizon, the incessant humming of the Cessna 172 Skyhawk's engine became almost unnoticeable, blending into the inherent rhythm of flight. The cockpit instruments glowed faintly against the darkening sky, while the last remnants of daylight illuminated the farmland, fields, and familiar highways below. It was a perfectly ordinary flight. A circuit the pilot had completed countless times; one he could do unconsciously. 

A sudden sputtering sound shattered the tranquility. The engine's steady whirring sound was replaced by an unsettling silence. The pilot glanced at his instruments to be greeted by a cascade of warnings- RPM was plummeting, a red 'ENGINE ALERT' box had appeared on his Primary Flight Display. If he didn't take action swiftly, disaster would be imminent. 

There was no room for panic, nor for an extended moment of disbelief. The aircraft still maintained a steady glide, but the circumstances had changed irrevocably.  The aircraft had lost all engine power, but it hadn't lost its ability to fly. The C172 could still glide, as long as the pilot maintained suitable airspeed and controlled the aircraft effectively. However, the distance it could glide was no longer under the pilot's control.

The pilot recalled his rigorous training. His priorities were clear. First, maintain control. He had to establish a controlled, unpowered glide before the loss of altitude catalysed by the constant descent became too difficult to handle. With the engine no longer producing the thrust needed to sustain a particular altitude, the pilot needed to adjust the aircraft's pitch to maintain the conducive glide speed. His primary goal was to maintain a safe descent while preserving as much of the aircraft's remaining energy as possible.   

With the aircraft stabilised,  the pilot began scrutinising the situation. Had the aircraft suffered a complete loss of engine failure or only a partial one? Was a restart possible? His eyes darted across the instruments panel, searching for an explanation. The tachometer suggested that the RPM was still dropping. The propeller continued turning, but only because of the aircraft's forward motion. The engine was no longer producing useful thrust. A quick glance at the remaining instruments offered no explanation for the failure.

The pilot resisted the urge to troubleshoot immediately, to find an explanation for the engine failure. He began working through the emergency procedures. Consulting the aircraft's engine-failure checklist, he attempted to restart the aircraft's engine, but to no avail. 

He reached for the radio microphone and declared an emergency, "Mayday, mayday, mayday, Cessna 172, engine failure, 45 minutes of fuel remaining, 1 soul on board, flight-level 30, position..." He reported the information available to him and conveyed his intentions. He also set his transponder to squawk 7700, the global general-emergency squawk code.

The response came only moments later. The controller acknowledged his distress call and began gathering the necessary information to assist the aircraft. He coordinated assistance on the ground and informed the pilot regarding available landing sites

With the emergency call made, the pilot shifted his attention to beyond the windshield. The fading sunlight had cast shadows on the once distinct fields, which were now barely visible and brutally indifferentiable. He needed a conducive landing site, and he needed one which the aircraft could successfully reach.

His eyes moved between the ground and the instruments. The altimeter indicated the height remaining between the aircraft and the inevitable terrain, while the airspeed indicator helped him monitor the glide. Every potential landing spot had to be assessed not only for its suitability but also for whether the Cessna could safely reach it.

A broad field to the left seemed promising, but its far end was bordered by trees. Another stretch of open farmland was visible farther ahead, but the aircraft certainly wouldn't be able to reach it. The nearest road seemed to be a good choice, but the power lines, houses, pedestrians and cars traversing made it far too dangerous a choice.

The pilot began narrowing his choices. He needed a sufficiently large, unobstructed, flat field, away from the rest of civilisation. He also had to consider wind speed and direction, as well as whether the aircraft could make it to said landing location. 

The aircraft continued its steady descent. The distance it could cover remained finite. The pilot could not waste any more precious altitude. Ahead, an open field seemed to be the most viable option. He carefully positioned the plane for a final approach; managing its airspeed and trajectory.  He relayed his intentions to ATC. Emergency services were on the way and assistance on the ground was being coordinated.

After consulting his checklists, with the field drawing closer, the pilot turned his attention to the final approach. The field grew larger by the second. He continued to make diminutive adjustments and corrections to his approach speed, pitch, altitude, and heading. The inoperative engine deterred any thought of a go-around or missed approach. This was his one and only chance.

 The pilot continued making minute corrections until the final few seconds, almost unconsciously. He flared the aircraft, and its wheels finally met the Earth. The C172 jolted as it rolled across the uneven field. He maintained directional control on the ground, in order to ensure that the aircraft stopped without colliding with any trees or other obstacles. For a moment, the cockpit was almost silent, only interrupted by the pilot's faint breathing and the sounds of the aircraft settling around him. Sirens sounded in the distance as emergency vehicles approached.

As the pilot completed the final actions of the 'Emergency Landing Without Engine Power' checklist, he glanced towards the approaching emergency vehicles and thought to himself, "Well, that's going to be a lot of paperwork."

The engine had not restarted- it did not need to. The aircraft was on the ground.

The Science

The Physics of an Unpowered Glide

An engine failure fundamentally changes the way an aircraft flies. With no thrust to overcome drag, it can no longer maintain its altitude indefinitely. It begins to descend, losing gravitational potential energy as it continues moving forward through the air.

However, the aircraft hasn't lost the forces that keep it airborne. Its wings still generate lift as air flows around them. By adjusting the aircraft's pitch to maintain a conducive airspeed, the pilot can control the descent and keep the aircraft gliding. The circumstances of said glide are determined by factors including drag, airspeed, and atmospheric conditions.

For the pilot, this relationship has consequences. Altitude becomes a finite resource that may be exchanged for horizontal distance. The pilot needs to find a conducive landing site before that horizontal distance runs out. How much distance? That depends on the plane's glide ratio and altitude. 

Glide Ratio

An aircraft's glide ratio, by definiton, describes the horizonal distance it can cover for every unit of altitude lost. 

Glide Ratio = Horizontal Distance ÷ Vertical Distance

A Cessna 172, for example, has a glide ratio of 9:1. This means that if the aircraft is flying at an altitude of 3000 feet, it can theoretically cover a distance of 27,000 feet horizontally. This is an idealised estimate, and the actual figure is also influenced by wind speed and direction, turns, and aircraft configuration.    

Best-Glide Speed

An aircraft's glide ratio depends significantly on its airspeed. Every aircraft has a 'best-glide speed', the speed at which it covers maximum horizontal distance for every unit of altitude lost. Flying too slowly increases induced drag (the resistance associated with generating lift), while flying too quickly increases parasite drag (the resistance caused by the aircraft moving through the air, which rapidly increases with airspeed). Both reduce the distance that can be covered during the aircraft's unpowered descent. At the best-glide speed, both of these forms of drag are perfectly balanced to produce the aircraft's maximum lift-to-drag ratio.

Distance Isn't Time

Glide ratio determines how far an aircraft can travel horizontally, but it doesn't cover how long it can remain airborne. That depends on its rate of descent, which is influenced primarily by airspeed, but also by the airplane's configuration and certain atmospheric factors.

For example, if an aircraft descends at a constant rate of 500 ft/min from 3000 feet AGL, it will take approximately 6 minutes (3000 / 500) to reach the ground.

For the pilot, both distance and time are imperative factors. A landing site may be within the aircraft's range according to its glide ratio, but it may leave little time for the pilot to assess the situation and prepare for an approach. Every decision must account for these factors. 

Conclusion

An engine failure eliminates the thrust that powers an aircraft, but the aerodynamic forces which keep said aircraft airborne remain active. The distance an aircraft can travel in an unpowered glide depends on its altitude, glide ratio, airspeed, and wind conditions.

The pilot must select a conducive landing site- one that is long and wide enough for an aircraft, without any obstacles, with a relatively even surface, and no threat to life- while being restricted by factors such as distance and time remaining. He or she must make these decisions under immense pressure, while juggling other tasks like controlling the aircraft and communicating with ATC, with only minutes on the clock.

When an airplane's engine fails, a race against time and faltering altitude begins. A pilot must make every second and every decision count.