As part of the FAA’s Fly Safe: Prevent Loss of Control Accidents national safety campaign, FAA officials are releasing tutorials on various topics that will help prevent Loss of Control (LOC) accidents. The latest topic is best glide speed.
A Loss of Control (LOC) accident involves an unintended departure from controlled flight. LOC can happen when an aircraft operates outside its normal flight envelope and could quickly develop into an aerodynamic stall or spin, surprising the pilot.
Contributing factors may include poor judgment/aeronautical decision making, failure to recognize a stall or spin and execute timely corrective action, or intentionally failing to follow regulations.
Inexperience in a particular make and mode of aircraft, lack of piloting ability, failure to maintain airspeed, failure to follow procedure or the use of over-the-counter drugs that affect pilot performance have also been cited as playing a role in this type of accident.
FAA officials note that many fatalities could be avoided if pilots were better informed and trained on how to fly at the best glide speed when preparing for a forced landing.
What is the best glide speed?
Best glide speed is the airspeed at which the aircraft glides the farthest with the least loss of altitude.
If faced with a forced landing situation, the best airspeed depends on what you’re trying to do. Are you looking to cover the greatest distance or the longest time in the air?
Here’s what you need to know:
Distance: Use the speed and configuration that will get you the most distance forward for each increment of altitude lost. This is often referred to as the best glide speed.
On most airplanes, it’s roughly half-way between Vx and Vy. Keep in mind that speed increases with weight, so most manufacturers establish the best glide speed at the maximum gross weight for the airplane. This means your best glide speed will likely be a little lower.
Time: If you need to stay in the air as long as possible to fix a problem or communicate your intentions and prepare for a forced landing, then you want the minimum sink speed. This speed is rarely found in the Pilot Operating Handbooks; it will be a little slower than the maximum glide range speed.
What about my airplane?
Plan to experiment on a flight with your Certificated Flight Instructor (CFI). Start at Vy, or the manufacturers recommended best glide speed with power off, and note the speed versus sink rate as you adjust pitch to reduce airspeed. You should be as close to mission weight as possible.
To identify minimum sink speed, look for the highest speed forward that will give you the lowest rate of descent.
Knowing these speeds will give you important numbers to have in the back of your mind if a situation ever warrants their use.
How far can I glide?
A rule of thumb for Cessna 152s and 172s is 1.5 nautical miles per 1,000 feet of altitude above ground level. Experiment to see how far your airplane can glide.
Tips for pilots
There is no substitute for frequent practice at typical mission weights. One trick is to choose a spot between the first and second third of the runway or landing area for an initial aiming point. If you determine that you can make that initial spot, add flaps and perhaps slip the airplane to move the aiming spot to the first third of the landing area. It’s better to land long than to stall or land short of the runway.
For a gliding approach, you’ll want to reach a key position from which you know you can make a successful landing during your base leg. Until the key position is reached, keep the airplane configured for best glide.
After you pass the key position, add flaps and gear to configure the airplane for landing and fly the final approach at 1.3 times the stalling speed in landing configuration (1.3 Vso).
When was the last time you practiced these maneuvers? They can help provide a better understanding of best glide speed when maneuvering to complete a forced landing.
- 90° power-off approach and landing
- 80° power-off approach
- 360° power-off overhead approach
- Overhead spiral approach
Did you know?
- Approximately 450 people are killed each year in GA accidents.
- Loss of Control is the number one cause of these accidents.
- Loss of Control happens in all phases of flight. It can happen anywhere and at any time.
- There is one fatal accident involving LOC every four days.
Learn more
The FAA Airplane Flying Handbook (Chapter 8) has several helpful diagrams for different power-off landing scenarios and corresponding key points.
The FAASafety.gov website has Notices, FAAST Blasts, online courses, webinars and more on key general aviation safety topics.
Check out the 2015 GA Safety Enhancements (SEs) fact sheets on the main FAA Safety Briefing website, including Flight Risk Assessment Tools.
The WINGS Pilot Proficiency Program helps pilots build an educational curriculum suitable for their unique flight requirements. It is based on the premise that pilots who maintain currency and proficiency in the basics of flight will enjoy a safer and more stress-free flying experience.
The General Aviation Joint Steering Committee (GAJSC) is comprised of government and industry experts who work together to use data to identify risk, pinpoint trends through root cause analysis, and develop safety strategies to reduce the risk of accidents in GA.
An FAA fact sheet outlines GA safety improvements and initiatives.
Slipping with flaps on a Cessna with fowler flaps has been a no no forever. The given and obvious reason is air flow over the the tail or perhaps better put the lack of air flow over the tail. Having flown many varieties of Cessna’s with fowler flaps I have to ask WHY would you have to slip with flaps ?
40 Degrees of flap on a Cessna is akin to selecting “express down” in an elevator ! The old saying that “you can never be too high in a Cessna” comes to mind.
Don’t miss understand, slipping is a great way to loose altitude, but given the effectiveness of Cessna flaps there is certainly no need for both at the same time and you most definately could take vital air awy from the tail surfaces and “wind up” (pun inteded) spiraling into the ground.
My 172M POH says,”Steep slips should be avoided with flap setting greater than 20 degrees due to a slight tendency for the elevator to oscillate under certain combinations of airspeed, sideslip angle, and centre of gravity loading.”
I have done maximum deflection sideslips with full flaps to test out this fable that people try to keep alive. There are no oscillations or any loss of rudder or elevator authority at all.
If there was any tendency for the plane to spiral out of control when put in that configuration, I think the Cessna POH would be more likely to read something like, “sideslipping with flaps is PROHIBITED” It is unlikely that Cessna would ever let a plane go into production that had those fatal tendencies in the first place.
Hi Nigel,
I’m not sure this should be called a fable. To your point of having tried it, I don’t doubt that you did it and obviously got away with it. That having been said I suspect that this line in POH came from the older Cessna 170B which as I’m sure you know has a very different tail. The “fable” has simply remained and perhaps Cessna could have/should have removed it for the 172 series, but I guess like me they figured it was worth leaving in.
However, having flown 170B’s, 180’s & 185’s in and out of some pretty short strips with challenging approaches I would ask why would you want or need to slip with 40 flap ?
In my experience if you are too high in any Cessna with fowler flaps your approach is in bad shape and the right hand might be wise to push the throttle foward and go around.
A fowler equiped Cessna with 40 flap drops like an in emergency down mode, if you need to loose more alltitude than that something is wrong…….in my opinion.
Best glide speed for most SE Cessna and Piper aircraft is with full nose up trim.
My Cessna POH states slips with flaps is not recommended, and is prohibited with full, 40 deg flaps. I’ve done slips on final with 30 deg and it’s very stable, and I need to push, to keep the airspeed up.
Check POH if slip is allowed with flaps!