Let’s say you are climbing in your PA46. What airspeed will you use to climb?
I bet the practical answer is something other than Vy (best rate of climb) speed. In the turbine versions of the PA46 Vy will gain the most altitude for a given amount of time, but the deck angle is uncomfortably high and the visibility over the nose is poor. In the piston versions of the PA46, Vy also provides the best rate of climb, but the engine cooling is less than optimal. At a slightly higher “cruise climb” airspeed it is much easier to keep the CHTs cool and the rate of climb is not appreciably lessened.
In both the piston and turbine versions of the PA46 I recommend 140 KIAS for climbing. This provides a lower deck angle, good visibility, and is well above the minimum icing speed of 130 KIAS. I know some of the piston owners will chant “my airplane won’t climb well at 140 KIAS!”, but the point is still valid…a higher airspeed than Vy produces better results in areas of consideration that are important to a pilot, and most pilots don’t climb at Vy, but rather at a higher “cruise climb” airspeed.
Most pilots won’t argue about anything I’ve related so far. The proof is in the pudding. It simply makes sense for the one paying the bills to keep CHTs low, and it pays to keep the spouse in the back happy by not having huge deck angles. Few argue about the “greater than Vy climb” because they can see tangible improvements in their pocketbook or the smile on the spouse’s face.
But best glide speed? Try to tell a bunch of pilots that flying anything other than best glide speed is a good idea and you’ll have an argument on your hands. I recently had a talk with a group of PA46 instructors about best glide speed, advising them that I recommend 110 KIAS for practicing engine-out landings. You’d have thought that I had committed “aviation blasphemy” for advising anything other than best glide speed in an engine out scenario. For some reason, arguments about best glide speed bring out the emotions.
If your engine fails, should you fly at best glide speed or some other speed? Climbing at Vy seems to be a non-emotional practice that most have a slight opinion about, but few will argue over. But should you always use best glide speed in an engine out situation? Oh my…toss that one out for discussion at the bar over a couple of beverages and watch the tempers flare and the pool cues swing.
With great anticipation for a lot of fun hate mail (or appreciation mail for a fun topic), I thought it good for me to dive into a headlong discussion about best glide speed, to break it down in minutiae and really dissect an engine out approach and landing. So, put the airplane in the hangar, open up your favorite beverage, and let’s talk about what to do when the prop stops but the wheels are not on the ground. But, leave the pool cue on the pool table…
According to the FAA Airplane Flying Handbook, Page 3-16, “the best speed for the glide is one at which the airplane will travel the greatest forward distance for a given loss of altitude in still air. This best glide speed corresponds to an angle of attack resulting in the least drag on the airplane and giving the best lift-to-drag ratio (L/Dmax).”
The “best glide speed” is published in your POH, but there really is not a best glide speed for your airplane for all situations. Read the above paragraph again…there is an angle of attack (L/Dmax) that provides the best glide ratio, not an airspeed. So, we need to fly an angle of attack (AOA) if you want to get the most distance for a given altitude. Most PA46s don’t have an AOA indicator, so we must approximate a speed that “gets us close” to L/Dmax.
To help you approximate L/Dmax, Piper listed a “best glide speed” in the earlier PA46s POH as 90 KIAS. But, this was simply an approximation. Best glide speed occurs at an exact AOA (L/Dmax), but the speed which provides that AOA is dependent upon weight and wind.
Here’s the unabashed propaganda you knew was coming…go buy an AOA for your airplane! I recommend the Alpha Systems AOA (https://www.alphasystemsaoa.com) that is mounted in your windshield viewing area. They offer an AOA that is mounted to the structural support in the center of the two windshields, and they also have a really cool HUD display that I love. It is mounted on the glare shield in front of the pilot. Flying an AOA is the right answer in so many phases of flight. If you are on the fence, I hope this article nudges you to the direction of investing in an AOA! And, no…I don’t make any money from any AOA vendors…I just think an AOA is a really helpful tool for the informed pilot in many phases of flight.
Piper listed 90 KIAS in the early piston PA46 POHs as the number that would be closest to best glide speed at maximum gross weight. So, best glide speed would be a bit lower for a lower aircraft weight. How much does your airplane weigh when the engine fails? Your guess is as good as mine, and we are both probably wrong. Neither of us will be exact, but neither will be far off. The point? One speed for best glide won’t work, or at least won’t work perfectly. Best glide speed in the early piston PA46s is not 90 KIAS, but 90 KIAS is a good approximation.
For the M600, Piper published a MUCH better POH, and it provides a range of airspeeds for best glide, all dependent upon aircraft weight. This is far more useful and accurate. From the M600 POH, the best glide speeds are listed as:
6000 lbs = 115 KIAS
5000 lbs = 105 KIAS
4000 lbs = 94 KIAS
There’s almost 20 knots of difference in recommended airspeed based upon weight. That’s a big range! The weight of the airplane definitely impacts best glide speed.
But wait…I know you are thinking right now…”Joe, you said that best glide speed is found at the L/Dmax AOA, not airspeed.” Right!! Best glide speed is always found at a L/Dmax, and that angle of attack is constant with changing weights. But, the airspeed required to fly L/Dmax changes. This is another good reason to buy an AOA for your airplane! It is easy to simply look at an AOA and pitch for L/Dmax.
Interestingly, there is a negligible glide range difference at varying aircraft weights. A 6000-pound M600 and an identical 4000-pound M600 will both glide the same distance if flown at L/Dmax (they will touch down at the exact same location), but the airspeed required to fly L/Dmax will be higher in the heavier airplane. So, the heavier M600 will arrive at the landing point before the lighter M600, but both will land at the same location. Interesting!
What about wind? Wind always affects best glide angle, just as wind impacts maximum range in cruise. To defeat a headwind, the pilot should always “lean into the wind” and when gliding with a tailwind, the pilot should slow down slightly. If the wind is great (over 25 knots in a PA46), a correction to best glide speed absolutely must be made to ensure the best glide angle.
There is a wonderful resource available that discusses best glide speed better than any other resource I’ve found. It is a book titled Aerodynamics for Naval Aviators (Page 369 to 373). This book is widely considered among aerodynamic professionals to be one of the masterpieces of writing on the subject of aerodynamics, and in my opinion should be on the reading list of every PA46 pilot.
A few more points before we assimilate the data into a useful discussion…
There is no way to “stretch a glide” if you fly your airplane at best glide speed (L/Dmax). If an aircraft is flown at L/Dmax, any increase in airspeed will increase the parasite drag and the aircraft will descend at a steeper approach angle (it won’t glide as far). Any decrease in airspeed from L/Dmax will increase induced drag and steepen the approach angle (it won’t glide as far). Bottom line, in an engine out scenario any attempt to fly any AOA other than best L/Dmax will result in a steeper approach angle (the airplane won’t glide as far). You simply cannot “stretch a glide” if you fly at best glide speed.
Another neat little tidbit of useful information…the AOA will increase as airspeed is decreased from L/Dmax due to an exponential increase in induced drag, and the AOA will decrease only slightly with an increase in speed from L/Dmax. Basically, if you fly a slower speed than best glide speed, the penalty is severe as induced drag (due to a much higher AOA) increases. So, if you want to “play it safe”, err to the high side of best glide speed, not the low side. Let me say it a little differently…if best glide speed for your airplane were 90 KIAS on a given day for a given weight and you glided 15 knots slower (75 KIAS), you’d have a much steeper approach than if you glided the airplane 15 knots faster (105 KIAS).
The key to understanding best glide speed is to understand angles. When your engine fails and you become a glider, you want to fly an airspeed that will provide the shallowest angle approaching the ground to glide the greatest distance. Since the birth of aviation, to know your approach angle in a glide has been nearly impossible to know through panel instrumentation available to most GA airplanes. But, recently there’s been a breakthrough in technology that allows you to know your approach angle definitively. That breakthrough is Garmin’s Flight Path Marker (FPM).
To have the FPM in a Garmin display, you must purchase Synthetic Vision and have Synthetic Vision enabled. I bet 95% of my clients that have a Garmin display have synthetic vision enabled, but I also bet that 70% of my client don’t know how to use the FPM and simply think “you just put the FPM on the runway when you land.” That’s a tremendous oversimplification, and shows that most pilots don’t know how to fly the FPM accurately. But, the FPM is simple to learn, and when the “light goes on” for the pilot in terms of how to fly the FPM in various phases of flight, the FPM will become a tool that you can’t live without.
The FPM that is displayed on most Garmin displays is singularly outstanding. In my opinion, it is so important that it makes upgrading to a Garmin display worth the investment in almost every situation. The FPM that is displayed on the Aspen products is almost not useable as it lags in processing speed and is displayed on a field that makes it hard to interpret. While I try to avoid endorsing vendors to our community, the FPM provided by Garmin on their G500 series, G1000 series, and G3000 series displays is singularly outstanding and in my opinion the only displays that provide the immensely useful FPM.
The FPM provides a plethora of good data to the trained pilot. With the FPM, holding altitude is a cake walk (just hold the FPM on the white horizon line), shooting an approach is greatly simplified (I’ll illustrate how to do this in a future article), determining the AOA is easy (the angle between the “airplane wings” and the FPM is the AOA), and the FPM can be a real life saver in an engine out landing because it shows you the glide angle.
The FPM literally shows you the airplane’s flight path. It shows you where the airplane is going at any time. So, it will show the approach angle in an engine out. Almost all precision instrument approaches have a 3.0 degree glide slope to the runway, and almost all VASI and PAPI approach slope indicators display a 3.0 degree glide slope. We are used to visualizing a 3.0 degree approach angle. You can insert the phrase “approach angle” anytime you see the phrase “glide slope”. The two terms are nearly synonymous.
Like I’ve stated, I really like to have an in-the-windshield mounted AOA. Because it is in the windshield, you can fly an exact AOA on an approach and not lose sight of your intended landing spot. But, if you don’t have a windshield AOA, should you fly an AOA with the FPM? I think not. To me, it is far easier to fly the FPM by contrasting it to the runway illustrated on the screen by synthetic vision. The FPM will show you the AOA, but you must either “do math” in the cockpit or “swag it” to fly the AOA displayed by the FPM. I’ll teach that lesson in a subsequent article.
So, what approach angle will your airplane fly in an engine out scenario? This answer is “it depends upon the airspeed held and the configuration of the airplane.” But with the FPM you can know exactly and manage the configuration and angle precisely.
The JetPROP is the only PA46 that can eliminate the variable of the windmilling prop when simulating an engine-out scenario. It is the only PA46 where the prop can be feathered without shutting down the engine. On all the other PA46s the instructor must pull back the power to simulate a “zero thrust” situation. In training, I usually use 160 ft/lb of torque in the turbine versions and use “back to idle, and forward about a 1/4” with the throttle on the piston versions when simulating an engine out scenario.
I’ve got to make a short diversion in this discussion to state the obvious. CFIs should NEVER shut down the engine in flight to simulate an engine out scenario. It is simply too risky. And, for the JetPROP airframes, I never have a prop feathered below 2000 ft AGL. Additionally, I only feather the prop in a JetPROP in VMC. Just saying…don’t let a CFI be a test pilot in your airplane.
Because the JetPROP propeller can be feathered, the JetPROP is the ideal PA46 to use to determine the approach angle when gliding at various airspeeds when simulating engine-out because it takes the prop out of the equation. In all the other PA46s the pilot must use a low power setting to approximate “zero thrust”.
Simply climb up to a safe altitude on a smooth day with little wind (I suggest climbing up to 10,000 AGL or higher to allow plenty of time to make lots of data recordings), pull back the power lever to idle, and feather the prop. The prop will slow down to about 400 RPM and the engine (Ng) will idle happily. Then, fly very exact airspeeds, allowing the instruments to stabilize, and note the approach angle as indicated by the flight path marker (FPM).
I suggest flying at 140 KIAS, allow the airplane to stabilize, make the recording of the descent angle. Then slow down to 130, then 120, then 110…you get the point, all while making recordings of your observations. Make recordings of the approach angle all the way down to 70 KIAS. There will be an airspeed where you observe the lowest approach angle, and that airspeed is the speed at which you will be flying “best glide speed” on that particular day for the weight and wind. It works flawlessly.
Now, climb back up to altitude and do the whole thing over again, but this time feather the prop, lower the landing gear, and add full flaps. Then, do the same test by checking the approach angle at various speeds starting with a speed just below Vfe for your airplane. Record those observations. You’ll notice that the approach angle is steeper with a gob of drag hanging out.
If you assimilate all of this data, you’ll find that a JetPROP is an amazing glider. On the day that I flew with Tom Thomason in his spectacular JetPROP in the Florida area on a beautiful day, our observations noted that his JetPROP can glide at about a 3.2 degree approach angle (clean configuration) at 90 KIAS all the way to about 11 degrees of approach angle at 110 KIAS with the gear down, flaps extended, and a full slip applied.
This means I can approach a runway from approximately any angle from 3.2 degrees to 11 degrees on this particular day in Tom’s JetPROP if the engine were to fail. That’s an enormous range of degrees, making the engine out landing super-easy for the informed and experienced pilot.
So, what airspeed should you fly if you experience an engine out landing? The quick answer is to initially fly the published best glide speed in your airplane. In the “heat of the battle” you’ll not be nearly as good as you think you’ll be, and immediately flying a published and known speed will help you immensely. This will assure the most range as you may want the most range in order to make it to the best airport to glide. Best glide speed gives you options and the best chance of making a long hunk of asphalt (a runway).
And airspeed control in an engine out landing is absolutely critical!! In an engine out landing, the left hand (the one on the yoke) controls airspeed. It is an all-important task of the pilot of a glider to use pitch to control the airspeed. Why? Because without a constant airspeed, a pilot cannot make assessments of the other variables of flight.
Here’s what the FAA’s Airplane Flying Handbook says about holding airspeed in an engine out glide:
A constant gliding speed is maintained because variations of gliding speed nullify all attempts at accuracy in judgment of gliding distance and the landing spot. The many variables, such as altitude, obstruction, wind direction, landing direction, landing surface and gradient, and landing distance requirements of the airplane, determines the pattern and approach procedures to use. Airplane Flying Handbook, page 8-26
So, in an engine out landing pitch controls airspeed, and maintaining an exact airspeed is critical. But, if pitch controls airspeed, it can’t control the approach angle to the runway. What controls the approach angle to the runway? The answer is drag factors.
To control the approach angle to the runway, the pilot must use landing gear extension (or not), flap extension (or not), spoilers (if installed), prop position, and a slip. If you are high on an engine out approach, throw out the gear, push the prop lever forward, extend the flaps and spoilers, and put your PA46 in a full slip. Or, use any combination of these factors to establish an approach angle that will allow you to make the runway. Pitch controls airspeed, drag factors control the angle that you’ll approach the runway.
Notice that I said “airspeed”, not “best glide speed”. It is critical that the pilot control the airspeed that is desired, and hold that airspeed in the descent. But, what speed is best?
I recommend you fly best glide speed until you are sure you have the ability to “make the runway”, or glide to the intended point of touchdown. Once you are assured that you’ll make the runway you selected, I recommend you increase your airspeed, and my suggestion is to fly 110 KIAS in all PA46s. Why?
There are several reasons. The first reason is applicable to all PA46s and is found on page 373 of Aerodynamics for Naval Aviators. Basically, there is little room for error if a PA46 approaches the ground at 90 KIAS. If you approach a runway at 90 KIAS, the round out (flare) had better be exact, or there will not be available energy to arrest the rate of descent. At 90 KIAS in a PA46 (especially with the flaps retracted), serious damage could occur to the airframe if the approach to landing is not flown well. There’s just no margin.
The approach angle in an engine-out landing is higher than a normal 3.0 degree approach angle, even if the airplane is flown in the completely clean configuration. If the PA46 is flown in a “dirty configuration” (gear extended, flaps extended, and a full slip), then the approach angle to the runway can be as high as 11 degrees, and even more if the piston PA46 has spoilers deployed and the prop pushed forward. Approaching a runway at a steep angle might be the exact right thing to do in some scenarios, and it certainly will not look normal unless you are well trained. If you approach a runway at a high approach angle at 90 KIAS (or less), there’s a strong potential that you’ll hit the ground far harder than intended, and it’ll probably bend many parts of your airplane.
We’ve had many PA46s crash during training due to a botched simulated engine out landing attempt with minimal airspeed. And, the accident record of actual engine out landings is not good either. We’ve had many accidents (including fatal accidents) where the botched landing attempt resulted in a stall/spin near the ground. An additional margin of speed above best glide speed provides margin from the stall/spin, which is the real killer in aviation.
There’s another good reason to fly a little bit faster than best glide speed (once the field is made) in an engine-out scenario…it increases your margin in case your approach makes you short of the runway. In an engine out scenario, you cannot “stretch a glide” if you fly at L/Dmax (best glide speed). It should not be much of a surprise that you won’t be “at your best” when handling any emergency, and you might somehow misjudge the winds, misjudge the approach angle, or fly the approach poorly. If you fly the approach at best glide speed and discover you are not going to “make the runway”, you simply will not have any option other than to “be short” and accept a landing off-airport. If you fly a little bit faster than best glide, you’ll have an option of pitching up slightly if you discover you are short of the runway and extending your glide.
As a CFI in our community, I train engine out landings at 110 KIAS, and I think other instructors should follow my example. Simply put, the additional airspeed protects the CFI but still allows the student to fly an approach with an exact airspeed, and the angle of approach to the runway is not significantly increased. The key in teaching engine out landings is to ensure the student controls airspeed with pitch and uses drag factors to approach the runway at an appropriate angle.
Interestingly, Beechcraft agrees with me. Now, I know Beechcraft is a whole other company than Piper, and I’m not trying to muddy the waters of where my passions exist. I love Pipers! I think Beechcraft simply chose to advise Bonanza aircraft owners and operators of something that Piper knows about, but simply chose to not advise PA46 owners and operators. Beechcraft lists a speed in their Bonanza POH’s called “Landing without Power speed” which is faster than “best glide speed”. Beechcraft knows that a little extra speed in the approach (assuming you’ve “made the runway”) to be a wise choice for many reasons.
Now, it needs to be said loud and clear that I don’t advise that you touch down your PA46 in an engine out scenario at 110KIAS! I also don’t subscribe that you touch down at best glide speed! This is a critical factor for all concerned. The faster you touch down, the greater the impact forces, and those forces are exponentially greater with faster speed. The POH in your airplane lists a speed to touch down in an engine out landing, and I am not advocating you touch down at a higher speed than Piper recommends. But, if you approach a runway appropriately with a higher approach angle (with drag factors applied), you’ll have no problem slowing the airplane down near the runway from best glide speed, 110 KIAS, or any speed in between. With the gear down, flaps down, and a slip applied, the PA46 will slow down very nicely so you can make your landing at an appropriate POH-recommended speed.
Before I get off my best glide soapbox, I’ve got one more factor that PA46 turbine pilots should consider. In a turbine, you might not be experiencing an engine failure, it might be a power rollback! In a turbine engine out scenario, the Ng will wind down, the prop will feather, and you’ll have a nice and comfortable (approximate) 600-700fpm rate of descent in which to glide to the ground if you fly at 100-110 KIAS. This is easily manageable.
If you have a power rollback, your turbine engine will roll back to idle and you’ll have no control of your engine with the power lever. The propeller will not feather and you’ll have a “windmilling prop”, which has a tremendous amount of drag. The increase in drag will cause you to have a 1600fpm rate of descent at the same 100-110 KIAS. That’s a huge increase in rate of descent (1000 fpm)! So, if you were to misdiagnose a power roll back as an engine failure (remember, you’ll not be “at your best” in an emergency) and not engage the MOR switch to control the engine, you’ll have a serious problem on your hands.
If you are in a JetPROP and try to fly 90 KIAS with a windmilling prop, you’ll have a LOT of disturbed air moving over the tail and the airplane will respond by the yoke shaking. It’ll feel much like a fully developed stall. If you fly a JetPROP at 90 KIAS with a power rollback and approach the ground, you’ll assuredly crash because of the incredible descent angle and lack of airframe energy to arrest the descent.
In training, I have pilots often misdiagnose an engine failure and a power rollback, and apply the wrong solution to the problem. I can happen. Again, in a real emergency you’ll not be at your best.
I hope this discussion helps with your understanding of energy management in an engine out scenario. In the next edition, I’ll discuss the importance of landing site selection and an in-depth discussion of how to fly an engine out approach with the FPM.
BTW…this article received a GOB of push back in the PA46 community of CFI’s and the hierarchy within MMOPA. Because I recommend CFI’s practice engine out landings in a PA46 at 110KIAS instead of the book-published 90KIAS, I’ve received all sorts of undesired backlash. But, I’ve had two astronauts, two PhD aerodynamicists, and two of the best glider DPEs within the FAA system review the content of this article to ensure that I’m putting forth accurate an important information. Of all the articles I’ve written, this one has received more scrutiny, both internal and external than any other 10X. I’m 100% sure about the content of my writing in this article, and I think this is an important subject within the MMOPA/PA46 community. I present it here not to be argumentative, but because I believe I have a responsibility as a leader in the PA46 CFI community, and this is a subject matter that has impacted me greatly. Bottom line, I’m passionate about it, and I’m right. Any stones that need to be thrown, throw them at me…I think the discussion is important and I have incredibly thick skin. I hope it helps…