Getting off, and on

Getting Off...............AndOn

June, 2002

What the Federal Aviation Regulations (FAR's) have to say aboutthe terms "landing and takeoff length" and "balancedfield length". Also a practical discussion on how specialtakeoffs and landings like "short field" and "softfield" are performed.

Size Matters

When it comes to runway length.

And wouldn't you just know it, but even runway length is subjectto a variety of terms, and is the basis of several FAR's .

FAR Landing And Takeoff Field Lengths

"The FAR landing and takeoff field lengths ... containcertain built-in safety margins to allow for unanticipated
situations. Brief and somewhat oversimplified descriptions ofthese distances for dry, hard-surface, level runways in zero-windconditions are given below." (Airworthiness Standards: TransportCategory Airplanes," FAR Pt. 25)

Landing Field Length

"The landing field length is defined by the Federal AirRegulations for transport-category aircraft. Briefly, the landingdistance is measured, horizontally, from the point at which theaircraft is 50 feet above the surface, in steady gliding flightat an approach speed not less than 1.3 times the stalling speed,to the point at which the aircraft is brought to a complete stopon a hard, dry, smooth runway surface." (Airworthiness Standards:Transport Category Airplanes," FAR Pt. 25)

"The FAR landing field length is obtained by dividingthe measured landing distance by 0.6 in order to account for thepossibility of variations in approach speed, touchdown point,and other deviations from standard procedures." "Certificationand Operation: Domestic Flag, and Supplemental Air Carriers andCommercial Operators of Large Aircraft," FAR Pt.121, paragraph121.195

Takeoff Field Length / Balanced Field Length

"The FAR takeoff field length, often called the FAR balancedfield length, contains certain inherent safety features to accountfor engine failure situations. This takeoff field length is definedin several slightly different ways... Briefly, if an engine shouldfail during the takeoff roll at a critical speed, called the decisionspeed V1, the pilot is offered the option of two safe coursesof action. He may elect to continue the takeoff on the remainingengines, in which case, the takeoff distance is defined as thedistance from the point at which the takeoff run is initiatedto the point where the aircraft has reached an altitude of 35feet. In the second alternative, the pilot may elect to shut downall engines and apply full braking."

"The decision speed V1 is chosen in such a way that thesum of the distance required to accelerate to V1 and then decelerateto a stop is the same as the total distance for the case in whichthe takeoff is continued following engine failure. If an engineshould fail before V1 is reached, the aircraft is usually broughtto a stop on the runway; whereas, if an engine fails at a speedgreater than V1 the takeoff is continued. The distances are basedon smooth, hard, dry runway surfaces." "Certificationand Operation: Domestic Flag, and Supplemental Air Carriers andCommercial Operators of Large Aircraft," FAR Pt.121, paragraph121.195

OK, enough of the dry stuff, let'stalk about getting it off...and on.

As you can appreciate from the above FAR's, we won't be talkingabout Transport Category aircraft in the following situations.This will be orientated toward the fun aircraft to fly- the GeneralAviation variety. When operating these aircraft you will inevitablycome across airports that will demand the maximum performanceof your aircraft. Factors that could be a consideration are treesat the end of the runway, snow, rough fields, short fields, andothers. Let's pick away at these one at a time.
As an aside, I am a strong believer in not abusing your aircraft,or it's powerplant(s). However, unusual situations call for pushingyour aircraft to the edge. Having said that to help clear my conscious,let's have at it.

Normal Takeoffs

As a foundation for the special operations to follow, let'sgo through a normal takeoff and landing, using our Speedmerchant500 twin-engine General Aviation aircraft.

As you approach the departure end of runway 29, your checklistis complete and you are cleared for takeoff. You roll onto therunway in a gentle turn and apply full power to the Speedmerchant500. Takeoff roll is normal, and you lift off some 3,000 feetdown the runway. In profile, your departure looks like this:

Well, that's not bad, and that's the way that most folks doit, but look at the displaced runway area that you left behind.Why not use that for takeoff? It's legal, and it certainly makesfor a safer operation. A couple of points though when you do this.If it is a tower-controlled airport, make certain that you advisethe tower when you call with your "ready for departure"radio call. Say something like "Oxford tower, 57 Golf isready for departure runway two nine, we want to back-taxi anduse the full length for departure." The tower does not expectyou to back-taxi, and they may have issued your takeoff clearancebased on the timing of landing aircraft and your using the "normal"runway departure. Not telling them can create anger up there inthe glass booth- and some heavily censored radio transmissiondirected to you. If you are operating at an uncontrolled field,always make a "blind radio call" when taking the runwayusing the CTAF- Common Traffic Advisory Frequency- for that field.Something like "Oxford traffic, Cessna 57 Golf is takingthe runway, runway two nine for departure, Oxford." If youare going to back-taxi, insert that in your call.

There is an old saying in flying: Thereis nothing more worthless than the runway behind you, or the altitudeabove you. Use all available runway for everydeparture.

Short-Field Takeoffs

The runway surface is OK, it's just short. Obviously, someoneflew the aircraft there in the first place, now it's your jobto get it back out again. First off, consider departing in themorning when the temperature is usually at its lowest for theday. Also, consider using a lower fuel load, of off-loading passengers,baggage or cargo.
Taxi out to the end of the runway. I mean the end of the runway.In a best-case scenario, the tail of the aircraft will be hangingoff of the end of the runway. If there is an over-run at the approachend of the runway, use it. The same applies if there is a displacedthreshold.

Check the area under the propellers. If necessary, get out ofthe aircraft and clear the area of any debris like rocks or smallstones. If you don't, these will be pulled up into the propellerarcs when you apply full power causing a ding in the blades whichcan lead to blade failure.

A "ding" in a propeller blade creates a stress areain the metal. Usually, these "dings" occur in the outer1/3 of the propeller blade where the most stress is. In a worst-casesituation, the stressed area will crack and the portion outsideof the crack will separate from the propeller. This causes anincredible amount of vibration. This vibration then puts moreloads on the engine mounts than they were designed for. In manycases the engine is torn off of the engine mounts before the pilotcan say "What the.....?"

Here's our runway:

Airspeed nomenclature

There are a couple of airspeed terms that we need to understand here.

Best angle of climb airspeed

This airspeed will put the aircraft into the air at its steepest angle- this is what you want to use on a short-field takeoff.

Best rate of climb airspeed

This one will give you the best rate of climb, but the angle will be less than when using best angle of climb. In other words, you'll gain more altitude per minute but will cover more ground in the process.

Both of these airspeeds will be in the aircraft Owner's Manual.

Back to our short-field takeoff. You're at the end of the runway.Set the parking brake. Stand on the toe brakes. Bring up fullpower smoothly, but smartly. When the engines have stabilizedat full power, disengage the parking brake, release the toe brakes,and roll. When you reach the Best Angle Of Climb airspeed pullback on the wheel and hold that airspeed. Go any slower and yourrate of climb will decrease, go any faster and your angle of climbwill decrease. Try not to turn the aircraft. Banking (turning)is inefficient from an aerodynamic standpoint, and it will decreaseyour rate of climb. Of course, if you're trying to avoid a hillstraight ahead, and head for a valley you have no choice.

Short-Field Landings

We'll look at two landings here: one with obstructions at theapproach end, and one where the approach area is clear.

Here's our first runway:

In a perfect world, you would make every landing at an airspeedof 1.3 times Vso, "stall speed, power off (with appropriateflap setting)." However, there are short runways out there,and many of them have obstructions at the approach end. So, inthis case, you will need to hang your behind out in the breezea little. Your approach speed will be slightly above Vso, perhaps5 to 10 knots. If it is turbulent out there, add one-half of thewind gust speed to your approach speed. In other words, if thewind is 20 knots, gusting to 30 knots add 5 knots to your approachairspeed.

You will need to be well set-up in advance for this approachYou should have the aircraft set at the descent angle and at yourtarget airspeed at least one mile from the runway. Establish yourairspeed with full landing flaps. Add power as necessary to holdthis speed Look at the end of the runway. Notice where it is inrelationship to the nose of the aircraft- this is important. Ifthe runway end is moving toward your reference point, you willovershoot the end of the runway and land long. If the runway endis moving away from your reference point, you will land shortand do a little tree trimming.

This is a difficult landing, and requires all of your skillsas a pilot. If at any time you are uncomfortable with how thingsare going, break off the approach and set-up again. Also, if thereis any wind, expect an "air bubble" as you cross overthe tree. It will normally push you up a little bit.

Once you cross over the tree, do not reduce your power- itgot you this far, it's going to get you to the end of the runway.If you decrease power prematurely you could very well stall anddrop the aircraft in. Just before touchdown, or immediately aftertouchdown, chop the power. Reach over and raise the flaps. Don'tbe hasty and grab the gear handle, it's been known to happen.Start heavy braking. Raising the flaps will transfer more weightto the gear, and make your brakes more effective.

Here's our second runway, with no obstructions at the approachend.

Hmmmm, notice something familiar here? With the exception ofno tree, and no displaced threshold, it's the same as the oneabove. Why would you want to come in at the same approach angleas you did when clearing an obstacle, the tree? Why not "dragit in" at a shallow approach angle and just chop the powerwhen you touch down? Good question. So, why? Ah, Grasshopper,physics.

Let's see what factors are in play as your aircraft approachesthe runway and you touch down.

Notice the "forward motion to dissipate after touchdown".This directly relates to your groundspeed at touchdown. Noticethat when "dragging it in" all of the airspeed is forward,and that when using a steep angle of descent some of the airspeedis forward, and some is vertical, due to your descent. The forwardmotion is less when using a steep angle of descent, and you willbe able to stop on the runway in a shorter distance.

And that, Grasshopper, is why you don't want to "dragit in" on a short runway. Pretty neat, huh?

Rough-Field Takeoffs

Let's say that your departure airport is "rough as a cob".The length is OK, it's just a very rough surface. Position yourselfat the end of the runway, and set the flaps for the maximum deflectionfor takeoff. Hold the brakes and bring up full power. So far,with the exception of maximum flap extension, this is pretty muchthe same as a short-field takeoff. Pull the wheel full back, rightinto your stomach.

Disengage the brakes and start your roll. Holding full backpressure on the wheel, allow the nose to raise off of the runwayas soon as possible. Once the nose comes off of the surface, easeup on the wheel so that the nose remains off of the runway butthe aircraft doesn't continue to pitch up. If you allow the noseto clear the runway any more than is necessary the aircraft willcreate considerable drag that will only lengthen your departuredistance.

The aircraft will lift off and start to fly prematurely becauseof ground effect- that "air cushion" near to the ground.For all intents and purposes, ground effect comes into play verticallyfrom the surface equal to the aircraft's wingspan. It is morepronounced in low-wing aircraft than in their high-wing brethren.This is an area where you have to exorcize considerable caution,as if you try to climb out of the ground effect the aircraft maystall and settle back down onto the runway. Allow the aircraftto accelerate while flying just above the runway.

Once the aircraft is at a safe airspeed, initiate a shallowclimb. When the aircraft is at least 500 feet above the ground,and preferably 1,000 feet, slowly retract a notch of flaps. Theaircraft will settle a little bit when you do this. Allow it tostabilize, and continue to slowly remove flaps in stages, waitingeach time until the aircraft has stabilized before proceeding.Pay particular attention to your airspeed throughout this exercise.After all of the flaps have been retracted, and the aircraft isstable, proceed with a normal climb out.

Rough-Field Landings

OK, you got it off, let's put this baby back on. Now's yourchance to drag the airplane in, unlike the caution not to do thisin short-field landings above. Approach the field in a shallowglide path, with full landing flaps deployed and sufficient powerto maintain airspeed. As you cross the end of the runway, slowlydecrease power but do not remove it entirely. Ideally, what youwant to do is have the airplane slowly settle onto the runwayat minimum flying speed. At touchdown you should have the wheelfull back to the stops, buried in your stomach. As soon as theplane touches down remove all power and continue to hold the wheelfull back. Leave the flaps extended as they will lighten the weightof your "footprint" until you slow down. When taxingback in, continue to hold the wheel full back to lighten to loadon the nose gear.

Snow on the runway

The amount of snow on a runway that your aircraft can handleis pretty much directly related to the size of your tires, andtherefor the size of your aircraft. It doesn't take much of thewhite stuff to make just moving on the surface of the field almostimpossible. Any more than a couple of inches of snow and mostsmaller aircraft simply cannot accelerate to a speed fast enoughfor lift off.

On landings, the snow will "grab" the mains and tendto slam the nose down prematurely. Unless it's just a light dusting,you are better off to wait until the plows have cleared the field-or June.

Ice on the runway

Ice is not as bad as snow- in some respects. If there is anyappreciable crosswind it's not a good idea to try either takingoff or landing. If the wind is down the pipe or calm, you cangive it a shot. Keep in mind, of course, that your braking abilitieswill be almost nil, and that if you have to abort your takeoffyour landing gear will most likely be removed as you proceed throughthe airport fence.

Having said that, I landed in Minnesota on a glare ice runwayin the 421B one cold February day. I was able to land at the endof the runway, and never used the brakes during the roll-out.Any turning motion was countered by using differential power onthe engines, as were all turns. Taxi speed was slower than a normalwalking pace, and I seem to recall my butt hovering several inchesabove the chair.

Summation

You may come across situations that require combinations ofall of the above techniques. The main thing is to understand whyyou are doing what you are doing, and how it effects the safeoperation of your aircraft. Keep in mind that any time you areoperating outside of the normal envelope you are putting yourself,and your aircraft, potentially in harms way.

Fly safely.

This tutorial is available on aCD

This tutorial, along with additional content, is availableon a CD. Click here formore information.

Hal Stoen

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