Saturday, December 15, 2007

Take Off Decisions in Single Engine Airplanes

Triggered by my review course, I was going to write an entry on V1, introducing it with a comparison to take-off decision making in single-engine airplanes, and multi-engine airplanes incapable of accelerating to rotation speed after an engine failure, but I quickly discovered I had enough to say about each to make this into three blog entries. So here's the first.

I'm returning to a common theme of this blog when I say that pilots spend much of our training and mental energy preparing for what might go wrong. One of the obvious things that might go wrong is for an engine to fail, and one of the worst places that could happen is just as we're taking off. We'd be at too low a speed to safely fly an aircraft, but at an unreasonably high speed to taxi, and the runway ends abruptly not far ahead. Any time spend pondering the best course of action could be very costly, so pilots work out in advance what the options are and at what point the options change, and then practice the hell out of them, so that should the worst occur, the hesitation before taking correct action would be no longer than the time to recognize the failure plus the reflex time required for mental intention to turn into muscle action.

An engine could fail at any point in the take-off sequence, from first applying take-off power to reaching a safe altitude after getting airborne. Which situation a failure places you in depends on what kind of airplane you are flying, where you were in the take-off sequence at the time of the failure, and the environmental conditions.

Clearly a single engine airplane that experiences an engine power loss on the take-off roll is in situation must stop the take-off attempt, no matter how little runway remains, or how close the airplane was to flying speed. The pilot's job is to quickly recognize the failure, retard the throttle to eliminate any remaining engine power, and apply the brakes as heavily as necessary in order to stop before departing a safe stopping surface. The checklist probably also asks the pilot to secure the engine at this time, too: shutting it down completely as well as closing the emergency fuel shut off valve and turning off the electrical master. In short: if the engine stops, then immediately stop the movement of the airplane, fuel and electricity. If the airplane is already airborne, then the checklist is almost identical, except that the first item on the list is "land straight ahead," which may involve extending flaps.

For the single engine airplane (or any airplane that loses all engine power after take-off) there comes a point in the climb out where it becomes possible to turn around and return to the airport rather than gliding to a landing straight ahead. This point is going to depend on aircraft weight, pilot skill, wind, runway configuration at the airport, and the terrain available for the straight ahead (or nearly so) landing. Some pilots memorize an altitude above ground level at which they can turn back. A good way to determine this is to actually practise it at altitude. Start in flight well above terrain and aligned with a geographical feature like a road or stream. Apply climb power and pitch to your take-off attitude. At an even thousand altitude, retard the throttle to idle. Immediately lower the nose to best glide speed and start a one-eighty degree turn. When you are re-aligned with the geographical feature and in a configuration that would allow you to land on it, check your altitude. Adding some as an allowance for any obstacles you'd have to maneuver around to actually get back to your departure airport, you now have an idea now of how much altitude you need to turn around. Obviously if you determine this with just you in the airplane at 4000' asl, the result isn't going to be sufficient with your family and baggage on board(*), or at a density altitude of 7000'.

It's not a simple problem and no one rule will work for every airport in all conditions. If straight ahead is only jagged mountains then what do you do? Some choose "don't use that airport." A controlled landing on almost any kind of terrain is safer than a stall-spin resulting from an unsuccessful turnback, and if you aren't going to be landing at the airport anyway, landing into wind gives you a slower, safer touchdown speed. Single engine pilots are also advised to pick a go/no-go point along the runway, such that if they are not flying by that point, they abort. That would allow them to recognize an underperforming engine or insufficient runway length while it was still an anecdote and not an accident.

There may be cases where a powerful single engine aircraft loses some engine power, but has enough power to, and the pilot deems it safest to continue rather than abort. I can think of two instances where people I know experienced a partial power loss immediately after take-off and chose to limp around the circuit on three cylinders. It's impossible to make all the decisions in advance. You have to follow a general rule that if there is any doubt in ability to take-off and climb over obstacles, abort the takeoff. If airborne, maintain flying speed above all else. If unable to maintain altitude and speed, land at the safest place you can reach without risking flying speed. Airspeed, as the old saying goes, is life. Altitude is life insurance.

*Yes, yes, glider pilots: I know that glide range isn't a function of weight, but stall speed is, and that's how single engine pilots die in this maneuver.


Anonymous said...

And to further complicate things, the "180" degree turn is actually more than 180 degrees because the aircraft must realign with the runway at the end of the turn. And of course the drag is higher in a turn so the descent rate is steeper. And the "ideal" angle of bank in terms of most degrees/second of turn vs. altitude loss is (as I recall) 45 degrees, and most of us aren't well-versed at doing such steep turns this near the earth unless you routinely fly crop sprays... I know some mission operations that work in very "difficult" terrain to say the least, and they've probably got this turn-back maneuver down to a fine art. For most of us the straight ahead (i.e. small turns only to find a clearing) will usually be safer until well into the climbout. At which point, depending upon climb rate vs. glide ratio, the runway may not be reachable anyway - ah the tough calls a pilot must make. That's why they get the 'big bucks' LOL

Aviatrix said...

That's exactly the kind of comment I was hoping for on this post.

CYOW + CYVR said...


PPRune thread on turnbacks.

Anonymous said...

I am a PP and I have been told that you NEVER turn back. You land straight ahead because it's safer. Could you please explain the thoughts behind your comment?


david said...

anonymous: 'never' may be a good thing to tell a post-solo student pilot — she already has enough to think about — but in real life, isn't there a point where you'd turn back if there were no other airports nearby? Would you still land straight ahead in a rough field if you were at 2,000 ft AGL on a straight-out departure? What about 5,000 ft? Remember that your departure climb angle is usually much steeper than your glide angle.

aviatrix: Another point to consider is big airports with more than one runway. When I was training in the north field at Ottawa (CYOW), the prevailing runway was 22. In case of an engine failure at low altitude, it would have been an easy matter to make a shallow left turn and land on 07 (8,000 ft), or one of the many taxiways, though there were also lots of fields straight ahead.

One of the nice things about single-engine planes is that they have slow enough stall speeds that an off-airport landing is not only survivable, but often results in no injuries or serious damage to the plane. Not always so with twins or other heavier planes, unfortunately.

david said...

cyow + cyvr: the PPRune thread on turnbacks is pretty sad, since it rapidly degenerates into a pointless debate about the downwind turn myth (have you ever posted on that, aviatrix?).

Aviatrix said...

Anonymous student: David's answer covers much of what I would have said. Obey your flight instructor. If you look at the linked PPRuNe thread and the Transport Canada document on stall-spin accidents referenced there, you'll see that turning back poses far greater risks than gliding to a landing nearly straight ahead. There are documented cases of airplanes gliding straight ahead to survivable landings even when there was no conscious pilot at the controls. You can find dozens of accident reports where student pilots who did everything else wrong (poor flight planning, got lost, didn't ask for help, and ran out of fuel) successfully completed straight ahead forced landings without injury. You can also find dozens of fatal stall-spin accidents resulting from pilots trying to turn back, or otherwise maneuver close to the ground.

But there are engine failures that occur after take-off at a sufficient altitude above both the runway and the surrounding obstacles that the pilot can turn back and land at the airport. I actually know someone who did two of those on the same day, (the aircraft turned out to have a roll of masking tape inside the fuel tank). He could have glided straight ahead, but there was only deep water and sharp rocks in that direction.

And by all means ask your flight instructor.

David: I haven't posted on the downwind turn or getting on the step (in the non-floatplane sense). I don't think I'll be returning to the airplane on treadmill story, either.

I'm going to leave this post as most recent one for a couple of days, because I'm really enjoying this discussion.

Mike said...

Great subject. Primacy is also a really important concept here. The first thing that you learn on a subject is often what you will do when the chips are down. I learned to fly 30 years ago in winch launched gliders. A cable break required quick action to get from a steep pitch up to Vbg before you stalled. Converting to powered a/c years later the first time an instructor simulated an EFATO I had a "reflex" reaction - bang the nose down from a Vx climb to maintain airspeed and then "what's ahead?". All that before I had thought what to do. Beacuse of that training 30 years ago.

It's also why instructors are the most important people on the planet! They are the people who embed these primary responses and they had better do it well.

I watched my 16 year old daughter manage 7 simulated engine failures in 0.7 hours the other day in 35 degree celsius heat as her instructor put her through the hoops. All flawlessly conducted and all a testament to good primary instruction.

No you can't instruct for every eventuality but you can sure increase the odds by getting the basics right and giving yourself the best chance in an engine failure situation.

Gee I love this blog.


nec Timide said...

The Aviation Safety Newsletter lead with the 180 degree return to airport in the 1/2005 issue.

There is also a letter to the editor about a recent fatal crash suspected to be a return to runway turn in the 1/2007 issue.

Anonymous said...

someone said: "Remember that your departure climb angle is usually much steeper than your glide angle."

Must be flying a Pilataus or Cessna Caravan? LOL Most light planes I've flown over the years would prove this statement wrong. A typical MTOW ROC might be 500 fpm. The typical descent rate with power off is at least this and more. After taking into account the turning required to get realigned.. . won't make it.

Now for taking off with a light single from a 12,000 foot runway - it should always be so easy.

CYOW + CYVR said...

David: Gene Spafford's famous commentary on Usenet[1] is just as relevant to PPRuNe as it ever was to Usenet.

[1] "Usenet is like a herd of performing elephants with diarrhea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind-boggling amounts of excrement when you least expect it."

gps_direct said...

I'll throw my 2 cents in with the idea of practicing the "impossible turn" at altitude. If you can line up with a road when you begin your "takeoff," you'll get a good idea of how far off centerline you'll be when (IF!) you can make the 180 turn. What's offset that far at your airport? At mine, depending on direction, turning one way aims at T hangars while the other way puts you into a forest/swamp.

Perhaps more importantly, pulling power in a Vy climb gives a good indication of how quickly and how much you have to PUSH to get the nose down before you bleed speed.

For instructors, why not (maybe not on the first flight, like my CFI did) point out likely landing zones for each departure runway. At some airports, a good spot can be mighty tough to find - you might even have to slip to get down to one in time...

Know your enviroment.

Inspector said...

Hi there. 'trix I often read your blog, and highly recommend it to my students. I don't often comment since by the time I read the post, most of the items that I would have written have already appeared.

I'm a flight instructor, and this past June, I experienced an engine failure in a single engine aircraft. I was flying in the circuit with my student, and after the 5th touch and go, the engine quit when I was turning crosswind.

I immediately turned the carb heat hot as I pushed the nose down to keep the airspeed. Seeing no suitable field in front of me, and having received a little bit of power from the engine, I continued the turn and brought the aircraft around for a slant final on the reciprocal runway.

I declared an emergency with tower, who quickly cleared me to land 'any runway' and gave me the winds. At this point, I wasn't sure that I was going to make the runway, but was hoping to make the airport property. The only reason that the aircraft touched down on pavement was due to the partial engine power and the tailwind.

Without conscious thought, I realized that my actions were aviate, navigate, and communicate, in that order. However, I was very concerned that I had just taught my student (by example) to return to the runway with an engine failure at low altitude. Therefore, I thoroughly debriefed him about the decision-making process involved, and the reasons why it was successful.

For those that are interested, the reason for the engine failure was mechanical. The exhaust baffles in the exhaust manifold came loose and blocked the exhaust. During the glide, some may have jarred away, allowing for partial engine power.

Thanks for putting together such a great blog, Aviatrix.

majroj said...

I'm not a pilot, but the USAF trained me to be the guy who ran up, shut it down and dragged the pilot out while big red (later, lime yellow) truck srayed us with foam. I heard about two turn-around crashes with unique aspects involving lost power on takeoff. Each occurred in Nebraska during extremely cold crosswind conditions.

The first was the crash of a Mexican DC-6 which would have held a trade delegation to Omaha, except they were in jail at the time (vice charge; too bad the entire crew wasn't as "unlucky"). The pilot took off for home without them, apparently following an informal SOP that full power from one engine was sufficient. This "didn't fly" (literally), and when they tried to come about they wingtipped into a frozen field about a mile from the civilian firefighters' closest unfrozen water source.

The other was a T-38 taking of eastbound from Offutt AFB's main runway, the wind gusting from the south to southeast. Just after rotation a little shy of the main intersection, apparently the #1 engine lost power; the pilot applied full throttle to the starboard engine but the plane had begun to veer to port and lose altitude. The port landing gear snagged and dragged a length of snowfence, causing more veer, drag, etc. It appeared the whole deal was going to veer enough to port to endanger the tower and point into the base town of Bellevue, but the pilot managed to steer it to a NW heading before the two fliers, as we used to call the maneuver, "un-assed the aircraft" via Martin-Baker seats. As the craft nosed down, the backseater went first and broke a leg due to low altitude canopy opening, frontseater did a 19G header into the frozen ground, followed and missed by the doomed aircraft, which nearly broke in half but did not burn.
Even when you have ejection seats, training and SOP are what's going to save the aircraft (knowing when NOT to fly) and the PAX (knowing when to get back to Dodge with or without the airframe around you).

Anonymous said...

I was in UPT and we were taught to
never take a problematic aircraft into the air. Even something far less of a problem than an engine failure can turn into a big problem real fast. If you have an engine failure before lift off always keep the plane on the ground
runway permitting. At a resonable speed before the runway ends do some S-turns down the runway to increase the time and distance to
the end of the runway but do very carefully or you could crash prematurely. Remember any landing
you can walk away from is a good
landing regaurdless of what happens to the airplane.