If you haven’t figured it out by now, I like to use a provocative”headline” to grab your attention, and sucker you intoclicking that button to read my column. The headline will generallybe related to the content, but in ways you might not expect.If you’re reading this, you fell for it!
Seriously, I’m beginning to get a case of heartburn over “stabilizedapproaches,” and I want to kick the subject around a little. I think there is widespread misunderstanding, it’s getting worse,and it is not safe.
The confusion comes from two different definitions of “stabilizedapproach.”
There is the “stabilized approach” for jets.
There is the “stabilized approach” for props.
They are not the same! For the record, I like them both- each in their proper place!
They are different because of the different characteristics ofthe two types of propulsion, and the different aerodynamics ofstraight and swept wings.
Even the FAA recognizes this, explicitly stating in all the PTS(Practical Test Standards) booklets:
The term “STABILIZED APPROACH” as used in thispractical test standard is not intended to be construed in thesame context as the term utilized in large aircraft operation.The term as utilized in this book means that the aircraft is ina position where minimum input of all controls will result ina safe landing. Excessive control input at any point could bean indication of improper planning. (FAA-S-8081-5C “AirlineTransport and Type Rating Practical Test Standards”)
That’s very simple. I think it means that if you have to start”yankin’ and bankin’,” or making big power changes toget where you’re going, it’s not stabilized (by either definition).
In my opinion, that “large aircraft” should read “jetaircraft.” In the FAA’s “corporate culture” today,”large aircraft” are jets, and way down at the bottomof the barrel are those pesky recips, which most in the FAA wishwould just go away.
Why Two Types of “Stabilized Approaches”?
D. P. Davies, author of the classic book “Handling the BigJets,” makes this very clear, subtitling his superb workwith:
“An explanation of the significant differences in flyingqualities between jet transport aeroplanes and piston-enginedtransport aeroplanes together with some other aspects of jet transportflying.”
Words are inadequate to express my admiration for this book.It should be thoroughly studied and re-studied by everyone flyingjets, even if the author can’t spell “airplane!” (Davies is,of course, British.)
Little Props and Big Props
Carefully, now. There are some very minor differences betweensmall and large prop aircraft, but essentially, the flying techniquesused in a Bonanza will serve well in flying a DC-6, and thosefor a Cessna 185 will work very nicely in a DC-3.
Little Jets and Big Jets
There are some very small differences between small jet aircraftlike the Citation or LearJet, and the “Very Large” aircraftlike the 747, but again, they are more alike than different.
Jets vs. Props
But as Davies points out, there are many, and very large differencesbetween “jets,” and “props,” and this is thearea I’d like to focus on in this column, with particular attentionto the “stabilized approach.”
In the Beginning …
Let’s start with a student pilot. Unfortunately, flying todayhas become very expensive, and very complicated by rules, by airspace,and by communications and new navigation techniques. Of necessity,it seems, we are spending less and less time on teaching goodold “stick and rudder” skills. We take the “canned”approach to the basic flying, keeping it very simple, while spendingmore time on the rules, talking on the radio, and handling ClassB airspace. All this with an eye towards getting the traineethrough the government-approved course in the minimum amount oftime, at minimum cost. Fifty years ago, it took forty hoursminimum to attain the Private, and the legal requirement remainsthe same today. Something “gave” in there, and I believebasic flight skills went down the tubes.
In the pressure to gain certification, certification itself oftenbecomes the only goal, and we forget the basic purpose of allthis, which is learning to be a pilot. Today, we don’t care howwell a pilot flies, as long as he knows the rules, communicateswell, and can handle Class B airspace.
One Size Fits All
The FAA hasn’t helped much, because they too have taken the “canned”approach by carefully defining the tasks and maneuvers neededto earn a Private, Commercial, or ATP certificate and associatedratings. The end result is that everyone, students and instructorsalike, begin to believe that once a trainee can successfully completethe highly “canned” maneuvers in the PTS with an examiner/inspectorwatching, he is fully qualified as a pilot at that level. I don’tthink so.
Take the student pilot, learning traffic patterns and landings. He is generally taught one “normal” configuration,one “normal” speed, and often, one “normal”power setting for the downwind, base, and final, from one “normalkey point” (abeam the numbers?). Or perhaps a differentsetting for each leg of the pattern. By default, anything andeverything else is “abnormal,” and “abnormal”to a student often equates to “emergency,” a “pulsepounder.” At some training airports, power-off approachesare nearly impossible, because everyone is playing “followthe leader” who is simulating a 747 pattern with a 152, withsome sort of idea about his own “stabilized approach.”
This is all fine for “initial training,” but the problemis that many of today’s pilots go on doing that “forever,”locked into a pattern enforced by their own ignorance, by the”traffic pattern nazis,” and by inexperienced CFIs,who themselves never learned anything outside “the usual.”
Or, take the instrument student, taught to make all approachesat one canned airspeed, power setting, and configuration, witha long “stabilized” final, perhaps from the outermarker. Only way to do it, right? Just like “the big boys,”right?
Simplification at the elementary level is fine, but unfortunately,I think too many pilots stay at the elementary level for far toolong. The first time SoCal Approach tells our new instrumentpilot “Bonanza 123A, maintain 120 knots to the marker, clearedfor the approach,” the pilot will panic, because he’s onlydone ILS approaches at 90 knots. The properly trainedBonanza pilot, when entering airspace like that, might helpfullyvolunteer, “SoCal, Bonanza 123A can maintain anything up to180 knots to the marker,” and then do it without a care inthe world, because he’s been trained (or has trained himself)to do whatever it takes. He’ll hit the GS at 180, reduce powerand start down, somewhere around 1,500′ or 2,000′ agl he’ll slowto gear speed, extend the gear, and finish up the final stagesof the approach at 100 knots, or 120 knots to DH. It’s not hard,you just have to do it a few times to pick up your timing, andget comfortable with it. You’ll also get a kick out of it whenSoCal says “Bonanza 123A, reduce speed to 140 now, you’reovertaking a 747.”
Does that approach qualify as a “stabilized approach?” Sure it does, in props, although I grant you, it may be approachingthe limits of the definition. You planned it that way, no unexpectedor large control inputs were needed, just one smooth maneuver,all the way. If the needles go peg-to-peg, or the airspeed dropsso badly that you have to jam on lots of power, then you get anoverspeed, and have to correct that, that is “unstabilized,”- in props.
When do we learn this “advanced technique?” It’s alittle hard to do it in the training for the instrument rating,because it runs up the hours needed, as well as the cost, andcomplicates getting the rating. However, once most pilots getthe rating, that’s the last they’ll see of an instructor untilthe next Flight Review or the next rating. It’s a dilemma.
OK, OK, Just What Is a “Jet-Stabilized Approach?”
The FARs do not help with the definition, nor does the AIM, forthis is only for jets, generally only in airline-type operations(I include 135 and corporate jets). The only place I know thatwe’ll see a definition is in the individual airline’s trainingprogram, or the company operating manual. There, you will finda near-universal, worldwide definition, which probably includesthe following for “normal conditions” (some wind correctionsto the speed exist, but let’s not clutter things up, here):
Gear Down, Landing Flaps set, all checklists complete,
On course, on glide slope (electronic or visual),
At the landing speed, in final trim,
Thrust set and stabilized to maintain all that,
All this is maintained from the defined point, right to the flare,only tiny corrections allowed.
All those requirements are required to be established and stabilizedat or above some stated altitude. If all that is not done and”stabilized” by the specified altitude, the pilot isrequired to execute a missed approach, and try again.I’ve never seen that altitude specified at less than 500′ agl(usually that low only for visuals), most airlines specify itin the 1,000′ agl range, and I’ve seen it specified as high as1,500′.
One simulator instructor I know can manhandle the 747 simulatorto a point at about 1,000′ agl on an ILS, let go of everything,slide the seat back, turn sideways, and fold his arms, while theairplane heads on down the ILS, and lands itself on the runway- without using the autopilot or touching a thing. Now, thatis a truly “stabilized approach” (for jets), in thestrictest sense of the term! That would be the ideal to whichall jet pilots should aspire, though they would do well not toslide the seat back, turn sideways, etc.
Why So Picky in Jets?
Now, this makes for a long, boring final. Why do we do it thisway? Early in the jet age, we lost several airplanes becausepilots tried to fly them like the prop airplanes they’d flownfor years. They’d come sailing down the ILS, bleeding speed offall the way, running the flaps out, gradually reducing thrust,cross the fence on speed at idle thrust, and land, thinking they’ddone a good job. Jets were so slippery, compared to what they’dbeen flying, they usually ended up fast, rather than slow.
But, a couple ended up in trouble. One scenario is where thepilot is “too high, too fast” and makes aggressive corrections,idle thrust, an early gear extension (noisy for the passengers!),more flaps, and sooner, maybe even cheating a little with speedbrakes, usually not used when flaps are extended.
He properly dives for the glide slope first, and gets on it, buthe’s still too fast, so he leaves the thrust at idle to slow down. Finally, the speed drops into the ballpark, everything fallsinto place, he heaves a sigh of relief, calls for the final checklist,and shoves the thrust levers up to “catch” the speed,just like he would have with big radials and props he’s flownall those years.
At that point, he’s dead.
Do you see the picture? Maybe a little cocky that he has “savedthe day” from that “hot approach,” he calmly pushesthe thrust levers up – and nothing happens! The early jets tookat least eight seconds to go from dead idle to any significantthrust, and eight seconds becomes infinity when you needed thrusta second or two ago. By this time, the speed is really dropping,because now he’s nose high, lots of drag, deep into the BackSide of the Power Curve. Next mistake, he’ll ease the noseup just a bit more in an attempt to keep things going while theengines do their agonizingly slow spool-up. But, a swept-wingjet is different from a prop airplane at that point, pulling thenose up will quickly kill more speed, which will dramaticallyreduce the lift, and the airplane will almost instantlybegin a high rate of sink, quickly building to thousands of feetper minute (if there’s room). A really good demonstration ofthis at altitude is terrifying, I cannot imagine the horriblefeeling of seeing it from a low altitude, in the final secondsof life.
(A side note here, this is not the so-called “deepstall,” it is simply a “high sink rate.” Differentanimals.)
What Did He Expect?
Let’s say this early jet pilot had just made the transition fromthe DC-6, or a Lockheed Constellation, both four-engine, reciprocating-engined,propeller-driven airliners. What did he expect of this shinynew jet, and why didn’t he get it?
There are a number of things, but the important ones are these. First, he was unable to get the drag he was accustomed to allhis flying life, which he needed to slow down. Jet engines atidle don’t make drag, like windmilling props do. Next, his jetengines did not respond instantly, as the big old radials wouldhave. Finally, even when the jet engines do spool up, they produceonly thrust, while the prop airplanes produce a large amount of”instant thrust,” and a lot of “instantlift” by blowing all that air over a very large portion ofthe wing. That sinking jet airliner can produce all the thrustin the world, but until that thrust is translated into morespeed (for lift), it’s going to keep right on sinking.
(Yes, some of the modern military aircraft can haul the nose tovertical, slam it into afterburner, and accelerate straight up,riding thrust alone, but we’re talking jet transports, here, withthrust-to-weight ratios of 1:3 or 1:4, not 1:1 or better.)
Grim picture. It took several crashes before the aviation industrysorted it all out, and came up with the procedures listed aboveto prevent this from happening again. The “Jet TransportStabilized Approach” has been highly successful – in jets.
For Jets Only!
I want to hammer the point home here that these “new procedures”were not improvements for flying in general, but differentprocedures, required only for the jets, because of theirdifferent characteristics. I make this point because I believesome or all of these “jet procedures” have filteredback down into the general aviation world, and are being usedin propeller-driven airplanes, usually unnecessarily, sometimesto the detriment of safety. In fairness, some partsof the jet procedures CAN be used in props with good results.
The solution to the problem (for jets) was primarily “TheStabilized Approach.” This set things up early, and it createda fairly high drag condition, so that a fair amount of thrustwas required to maintain flight. By doing this in jets, we stayaway from idle thrust (when close to the ground). A key pointhere is that jet aircraft can afford to do this, because theyhave a huge margin of thrust available at low altitudes, and evena small amount of additional thrust is sufficient to blast themright into the go-around, even with gear down, full flaps, andeven an engine out. Any variations in thrust required to flythe glide slope are always well above idle.
Most (all?) jet aircraft were also modified with a “highidle” setting triggered by any flap extension, so that evenif the pilot pulled the thrust levers all the way back with anyflaps at all, the engines would idle fast enough to be able toaccelerate very quickly to maximum thrust. Good modification,I think. If only the early 727 had had it, we might not evenbe having this discussion today.
Turning to Props (Including Turboprops)
Assume a light single, stalling speed about 60 clean, about 55with full flaps. I have seen people slow down on the 45-degreepattern entry, get the gear down, and set half flaps, slow toabout 80 or 90, and get their checklist done. Good procedure,right? You’ll fit right into a busy training pattern, and don’thave anything left to do but extend final flaps. You may evenbe forced into this, if the pattern is really busy. “Ifyou gotta, you gotta,” but that doesn’t mean it’s a goodidea everywhere, all the time. It may well be a good procedureif you’ve never flown a complex airplane before, or the particulartype.
Oops, the Engine Just Quit
What’s wrong with this approach? Well, try failing the engine. You will find that with all that drag, and such a slow speed,you’ll have to shove the nose down hard to maintain anydecent speed, and from 800 ft., you’ll be in the trees beforeyou know it. You might get to choose which tree, but you won’thave many options. If you do this with a twin, and an enginequits, you’ll need to not only handle the engine failure, butget the flaps and gear back up for single-engine flight, thenonly seconds later put them right back down again, for the landing. See how that affects your workload! And, where does it leaveyou on your checklist? Is this the best we can do?
Why not come “coasting” into the 45 at 120 knots, oreven 150, “clean?” That “stores energy,”so that if the engine quits, you have far more time, and far moreoptions than the trees right below you. With only a small modificationto the pattern, you may even have enough energy left to make yourintended runway. If you really feel this is hazardous when mixingit up with the trainers, then how about using the “high performance”TPA (Traffic Pattern Altitude) of 1,500 ft.? If you do this,you’ve got another 700 ft. of altitude to play with, too! Ifyou’re going to use the speeds of the “large aircraft,”doesn’t it make sense to use their TPA, too? There’s rarely anyonethere, and from that “high perch” you can see the littleones below, and can pick your “slot.”
OK, here we are on the downwind, abeam the numbers, speed stilldropping, low power, and there’s no one ahead of us. Gear down,complete the checklist, play the turns so that you need no additional power to get to the runway,adding flaps as needed when the speed gets too low without them. Play this so that you touch down on the numbers, a few knotsabove the stall. Any time during that approach, if the enginequits, you might skip the flaps (drag), and still make the runway. Pulling the prop all the way back will extend the glide, andif you’ve got quick gear, pulling it up will assure making thatnice runway, even if you do put it on the belly. That’s a wholelot better than an off-airport landing.
Yes, that means a “decreasing speed” approach, all theway. That’s utter anathema in jets, but highly desirable in props,in my opinion.
Same thing for an ILS. Shoot it at 120 or better, as clean asyou can, maybe with only the gear down (gear up will work, butit gets a little busy at DH). Make sure you keep it on, or abovethe glide slope, there’s not a thing in the world wrong withdeliberately flying the glide slope a dot or more high, it won’tmake you go blind, and it won’t grow hair on the palms of yourhand. That extra angle gives you “more energy.” Breakout at DH, power off, handle the drag to land as you did above. If this forces you to land a little long, so what? Most ILSrunways are plenty long enough to land in the last third, andthe big jets aim for the 1,000 ft. point, are prohibitedfrom touching down in the first 500 ft. Why are some of us soanal about planting a Bonanza on the very end?
No Flaps, Please
Oh, you don’t like that last-minute configuration change, yousay? Fine, land without the flaps, then!
Why do we use flaps so much, and so often, anyway? Thedifference in the stalling speeds of a 182 between “FullBarn Door” flaps, and no flaps at all is all of just SIXKNOTS! Check the POH for one of the light trainers, you’llfind it’s often down in the TWO KNOT range! Usingfull flaps tends to make the airplane land nosewheel first, itmakes the elevator forces very heavy in some (Cessna 182), andif you trim too much, it makes the airplane pitch up too hardon a go-around. All are traps that can be avoided by landingwith partial flaps, or none at all. Go out and shoot some landingson a nice calm day, using varying degrees of flaps, with an eyetowards speed at touchdown, and landing roll. Take an observeralong, and have him call the GPS speed, so you’re not misled bystatic error in the IAS, caused by the different attitudes. Thenc’mon back and tell me just why so many use full flaps on a 10,000ft. concrete runway? Yes, if you’re planning to put that 182into a 600 ft. strip, then you probably want full flaps, and somepractice, too, before you do it.
Becoming a Pilot, At Last
There is another benefit to all this. By flying your airplanein a variety of ways, you learn more about your airplane, andmore about yourself. You extend the performance envelope. Thatis “a Very Good Thing,” and is another step towardsmaking you a “Real Pilot,” instead of just someone witha certificate. There are lots of certificates out there,but we’re running short of pilots.
Be careful up there!