Glide Performance
Expected Glide Performance drives airfield suitability decisions and impacts the conduct of the approach and landing.
Introduction to Glide Performance
- Expected Glide Performance drives airfield suitability decisions and impacts the conduct of the approach and landing.
- Ultimately, glide performance translates into options for gliders or aircraft in the event of an engine-out situation.
- Reinforce your understanding of Glide Performance by completing the knowledge quiz and interactive scenario, comparing your performance with the applicable Airman Certification Standards, and reviewing the topic summary before moving on.
Glide Performance Key Highlights
- Glide performance describes the aircraft’s ability to maintain distance and control while descending without engine power.
- Best glide speed provides the maximum glide distance for a given aircraft weight and configuration.
- Glide ratio compares horizontal distance traveled to altitude lost during a glide.
- Aircraft weight affects glide speed but does not significantly change the glide ratio in still air.
- Wind conditions influence actual glide distance over the ground and should be considered during emergency planning.
- Improper aircraft configuration, excessive drag, or uncoordinated flight can reduce glide performance significantly.
- Best glide speed typically increases as aircraft weight increases.
- Pilots should establish and maintain best glide speed promptly following an engine failure or power loss.
- Terrain, obstacles, and landing area selection are critical considerations during glide operations and emergency descents.
- Understanding glide performance improves emergency preparedness, decision-making, and forced landing outcomes.
Best Glide Versus Minimum Sink
- Best glide speed provides the greatest distance through the air for a given altitude loss in still air.
- Minimum sink speed provides the greatest time aloft by producing the lowest rate of descent and is normally slower than best glide.
- Achieving either result requires the proper airspeed and aircraft configuration specified by the pilot's operating handbook (POH).
Glide Ratio
- The glide ratio is the ratio of the distance an aircraft travels to the altitude it loses.
- An aircraft that travels 50' horizontally for every 10' of vertical altitude is said to have a glide ratio of 5 (50/10).
- Factors that impact glide distance include wind, configuration, and technique (i.e., pilots must avoid uncoordinated flight, which increases drag and reduces glide distance).
- Best glide occurs at or near maximum lift-to-drag ratio, where total drag is minimum; induced and parasite drag are approximately equal, but neither component is individually at its minimum.
- For a typical rigid-wing airplane in the same configuration, increased weight raises the speed for best glide and the descent rate while the ideal still-air glide ratio remains approximately unchanged.
Glide Performance
- An aircraft with a glide ratio of 5 has a descent angle of 11+ degrees, meaning if you lose an engine on a 3° glide slope, you cannot reach the runway, regardless of altitude.
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Effects of Winds:
- At a fixed airspeed and configuration, a headwind decreases range over the ground because it reduces groundspeed during the available glide time.
- At a fixed airspeed and configuration, a tailwind increases range over the ground because it increases groundspeed during the available glide time.
- Aircraft-specific guidance may call for a different optimum speed in headwind, tailwind, or sinking air. Do not invent a universal correction for an airplane.
Calculating Best Glide Speed
- Refer to POH for the best glide tables.
- Best glide occurs at or near the highest lift-to-drag ratio. In many light airplanes the published value falls between Vx and Vy, but that relationship is not a substitute for aircraft-specific data.
- As an aircraft becomes lighter (i.e., as an aircraft burns fuel), the best glide speed reduces as well.
- Manufacturers typically publish the best glide for a given gross weight, and the best glide will decrease as the aircraft's weight decreases.
- Pitch for best glide by controlling the nose to achieve the published speed.
- Know the aircraft's approved or recommended power-off speed, configuration, and checklist before flight. Do not substitute a generic pitch attitude or trim position for unavailable aircraft-specific guidance.
- No matter the technique, be mindful of stall conditions.
Calculating Minimum Sink Speed
- The minimum sink may not be in most POHs, but it is generally slower than the best glide speed.
Applying Glide Performance to a Forced Landing
- After a power loss, maintain control and promptly establish the aircraft-specific glide appropriate to the objective and conditions. Best glide normally preserves maximum still-air range; minimum sink normally preserves maximum time.
- Select a landing area with margin and continuously reassess reachability using actual wind, terrain, obstacles, configuration, aircraft condition, turns, coordination, and observed progress. A glide ring or published ratio is an estimate, not a guarantee.
- Turns increase load factor, required lift, drag, and altitude loss, and they raise stall speed. Include turn losses and stall margin rather than planning from a wings-level glide ratio alone.
- When low, maintain an appropriate airspeed, minimize unnecessary drag and maneuvering, and use a reachable touchdown area. Pulling back to stretch the glide increases induced drag and stall risk.
- When high and the landing area is assured, use aircraft-appropriate pattern changes, slips, turns, or drag devices to manage excess energy while preserving limitations, obstacle clearance, and a stabilized final approach.
- Landing gear, flaps, a windmilling propeller, contamination, uncoordinated flight, and other drag sources generally reduce range. Follow the AFM (Aircraft Flight Manual), POH, or emergency checklist because recommended configuration and propeller actions vary by aircraft.
Avionics and Electronic Flight Bag Tools
- Some avionics and EFBs (Electronic Flight Bags) provide glide rings based on the (albeit limited) flight conditions.
- These range rings are estimates only.
- Setting avionics ranges to the anticipated glide distance also provides an idea of the available options (i.e., if no airports are within that distance, any need to land will be off-airport).
Glide Performance Interactive Scenario
The Field Beyond the Highway
Manage an actual power loss from cruise as best-glide speed, wind, weight, drag, turns, field geometry, restart workload, and landing configuration compete for limited altitude. Abbreviations used in this scenario: Mean Sea Level (MSL).
Decision 1
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Scenario Complete
Glide Performance Knowledge Check
Choose the knowledge check that matches your current training for Glide Performance.
Private Pilot
PPL knowledge check
Core Knowledge Review
Review foundational knowledge, key concepts, and practical considerations. Topic: Glide Performance.
- Immediate feedback
- Answer explanations
- Account progress tracking
Commercial Pilot
CPL knowledge check
Advanced Application
Apply knowledge to advanced operations, risk management, and aeronautical decision-making. Topic: Glide Performance.
- Immediate feedback
- Answer explanations
- Account progress tracking
Why Take a Quiz?
Quizzes reinforce key concepts, identify knowledge gaps, and build confidence for real-world decisions. Quiz material is representative of the information provided here and is not based on or sourced from the Federal Aviation Administration test bank.
Glide Performance Lessons & Case Studies
- National Transportation Safety Board Identification: ERA24FA365:
- The NTSB determines the probable cause(s) of this accident to be: A total loss of engine power for undetermined reasons. Also causal was the flight instructor’s failure to maintain adequate airspeed during the forced landing attempt, which resulted in exceedance of the airplane’s critical angle of attack and an aerodynamic stall.
- National Transportation Safety Board Identification: ERA24LA011:
- The NTSB determines the probable cause(s) of this accident to be: A total loss of engine power for reasons that could not be determined. Contributing to the accident was the flight instructor’s failure to maintain adequate airspeed and exceedance of the airplane’s critical angle of attack during the forced landing, which resulted in a hard landing.
- National Transportation Safety Board Identification: CEN23FA258:
- The NTSB determines the probable cause(s) of this accident to be: The pilot’s improper preflight fuel planning and inflight fuel mismanagement, which resulted in a total loss of engine power due to fuel exhaustion, and his subsequent failure to maintain adequate airspeed during the forced landing, which resulted in the airplane exceeding its critical angle of attack and entering an aerodynamic stall at a low altitude. Contributing to the accident was the pilot’s impairment from his use of multiple impairing substances.
- National Transportation Safety Board Identification: WPR22LA080:
- The NTSB determines the probable cause(s) of this accident to be: A partial loss of engine power due to an obstructed catalytic converter, which most likely resulted from the pilot’s failure to properly repair or replace it after it was likely damaged during a previous incident. Contributing to the accident was the pilot’s failure to maintain adequate airspeed during the forced landing, which led to an exceedance of the airplane’s critical angle-of-attack and an aerodynamic stall.
- National Transportation Safety Board Identification: CEN21LA401:
- The NTSB determines the probable cause(s) of this accident to be: The pilot’s failure to maintain airspeed during a forced landing, which resulted in the airplane exceeding its critical angle of attack and a subsequent aerodynamic stall. Contributing to the accident was the loss of power due to the failure of the engine’s drive belt.
- National Transportation Safety Board Identification: CEN17LA228:
- The NTSB determines the probable cause(s) of this accident to be: A total loss of engine power due to the engine’s unresolved high operating temperatures, which resulted in failure of the distributor rotor and drive shaft, and the pilot’s failure to maintain airspeed during the subsequent forced landing, which resulted in an aerodynamic stall and loss of control.
- National Transportation Safety Board Identification: ERA17FA140:
- The NTSB determines the probable cause(s) of this accident to be: A loss of engine power for reasons that could not be determined due to postcrash thermal damage to the engine accessories and the airframe. Contributing to the accident was the pilot's failure to navigate to any of the available forced landing sites within gliding distance of the airplane following the loss of engine power.
- National Transportation Safety Board Identification: GAA16CA495:
- The NTSB determines the probable cause(s) of this accident to be: The pilot's failure to maintain adequate airspeed and his exceedance of the airplane’s critical angle-of-attack during a simulated engine failure and forced landing with a tailwind, which resulted in an aerodynamic stall.
- NTSB Identification: ERA19FA106
- NTSB report summary: After a simulated engine failure shortly after takeoff, the left engine lost power for an undetermined reason. The instructor's low-altitude exercise left little margin to configure the airplane for single-engine flight; airspeed decayed during the attempted forced landing and control was lost.
Glide Performance Conclusion
- As a rule of thumb, any aircraft should be able to glide to a distance of approximately 45° down.
- If, when gliding, the point of intended landing is moving higher in the windscreen, the aircraft will land short of the intended point.
- Understanding glide performance is a regular part of flying a glider.
- What's not so normal is considering how it applies in a powered aircraft when the power is no longer there.
- Understanding glide mathematics helps pilots make faster and more accurate emergency landing decisions.
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