Learn & Understand

The Gimli Glider and Best Glide Speed: Glide Ratio in a Real Emergency

Glide ratio is normally a planning number pilots memorize and rarely test in earnest - but on rare, well-documented occasions, it has become the single number standing between a safe landing and disaster, with no engine power at all to fall back on.

The Gimli Glider: A Real Test of Glide Ratio Under Pressure

In July 1983, Air Canada Flight 143, a Boeing 767, ran completely out of fuel at cruise altitude due to a fuel quantity calculation error connected to a unit conversion mistake during refueling, leaving the crew to execute a genuine unpowered "dead-stick" descent and landing with both engines shut down. The captain, drawing on his own separate experience as a glider pilot, used the aircraft's known glide ratio to judge whether it could reach a suitable landing site, ultimately gliding the aircraft to a safe landing on a decommissioned runway at Gimli, Manitoba - an event now widely referenced in aviation training precisely because it demonstrated glide ratio's real, literal life-or-death planning value, not just as an abstract textbook figure.

Best Glide Speed: Why Flying Faster or Slower Both Cost You Range

The glide ratio figure quoted for an aircraft type, and the underlying lift-to-drag ratio it represents, is only achieved at one specific airspeed for a given weight and configuration, commonly published as "best glide speed." Flying faster than best glide speed increases drag disproportionately, causing the aircraft to lose altitude faster relative to the ground distance it covers - reducing effective glide ratio and range. Flying slower than best glide speed approaches the aircraft's stall speed margin (as covered in this category's stall speed guide) and also increases induced drag as the wing works harder at a higher angle of attack to generate the same lift at lower speed, again reducing the effective glide ratio actually achieved compared to the published best-case figure.

Why This Makes Best Glide Speed Critical Emergency Knowledge

Pilots are specifically trained to memorize and immediately fly their aircraft's published best glide speed the moment an engine failure occurs precisely because of this sensitivity - a pilot who instinctively flies faster (out of an understandable urge to "get down quickly") or slower (out of an instinct to conserve altitude by flying gently) than the published best glide speed will achieve meaningfully less real glide range than the aircraft's rated glide ratio promises, exactly the margin that mattered so directly in the Gimli Glider's successful outcome.

Applying This to a Calculated Glide Ratio

A published or calculated glide ratio figure represents a best-case number achieved only at the specific best glide speed for that aircraft and configuration - any real emergency glide planning needs to account for actually flying that specific speed, not just knowing the glide ratio number itself, exactly the practical distinction that separated a textbook glide ratio figure from the real, successful outcome at Gimli in 1983.