Over the past several months I spent time in this space tackling the issues and procedures involved in establishing and flying holding patterns. Fairly dry stuff, certainly nothing to excite much controversy. Lets change that. Lets do the interrelationship between pitch and powera subject guaranteed to light fires in the hearts of the faithful.
Although it is clear to most pilots that pitch and power affect both speed and altitude, there are times when it is useful to mentally assign a primary chore to each. Final approach is one such area. If you learned to fly, as I did, anytime before the mid-1970s, your ideas on the subject of pitch and power are likely to be at significant odds with those of more recent graduates. The earlier group adheres, sometimes fervently, to the belief that power controls altitude and pitch controls airspeed. The later group is more likely to have been taught the reverse.
To expand a bit, at its extreme the classic teaching technique holds that all altitude discrepancies on final approach should be dealt with exclusively through power adjustments and that pitch changes should be reserved for managing airspeed. To put this in context, imagine an aircraft on a VFR final approach, on glide path but ten knots fast. Pilots trained as described are most likely to raise the nose in response to the excess airspeed, wait for the speed correction, then reduce power in order to correct the somewhat high glide path created by the original pitch change.
The second, more "modern" group adheres, perhaps unknowingly, to principles currently advanced by the FAA. The teaching sounds like this: with some notable exceptions, power most directly controls speed and pitch controls altitude. In the same approach situation cited above, pilots trained in these principles would reduce power on discovering the airspeed excess, then raise the nose as necessary to counter the degrading descent path.
Since both groups eventually end up in the same place with the same end productsreduced power, increased pitchit may seem trivial to argue the relative merits of the differently sequenced inputs. Put another way, despite their differences, both groups appear to get the job done.
Despite the appeal of this apparent logic, there really is a right and a wrong; pitch and power changes are not trivial subjects, and proper mastery can make flight significantly easier. Although the rewards of a precise approach to the inputs are greatest in IFR flight, here are several VFR examples in support of the argument that there is a "right/wrong" to the subject. All apply to the typical light general aviation aircraft being flown at an airspeed at least 1.3 Vso.
For the first, imagine this situation: you are on downwind leg, precisely at altitude, offset exactly the right distance from the runway, overtaking the 152 ahead in the pattern.
You need to slow down. What should you do first, reduce power or raise the nose? Both will have the desired effect on speed, but one is obviously wrong: you do not want to climb, the inevitable result of starting out with a pitch change. The better answer is to reduce power and then gradually raise the nose to remain on altitude while slowing down.
The second example: you have leveled off at your cruising altitude, set the power precisely and adjusted the trim. Over the next few seconds, you see your plane starting a slight descent. How would you arrest the descent, power or pitch? The logical action would be to start by raising the nose. NOTE: this answer refers exclusively to the action necessary to arrest the descent, not the procedures necessary to eventually climb back to the desired cruising level.
A third: you want to do a loop. Yes, a loop. After building the necessary airspeed, how should you startby lifting the nose, or by simply adding more power? Ill leave the answer to you.
Finally, and the example most likely to step on a few preconceptions: you are on short final, on speed, but on a glidepath that is aimed somewhat short of the runway. In other words, you are getting "low." What do you choose for your initial reaction, raising the nose or adding power?
To those who answer "power," my response is that the input is counter-intuitive: the airplane is most obviously pointed in the wrong place, why not correct that?
Because, you might argue, the plane will slow down dangerously if you pull up. Yes, over timeif thats all you do. But, equally, if all you do is add power, the plane will crash short of the runway, going a bit faster. You need to do two thingscorrect the pitch, maintain the speed: which sequence of inputs is most intuitive?
I teach students in this circumstance to raise the nose to correct the glidepath and to add power to maintain airspeed, simultaneously, if the student is sharp enough, as neither input without the other is going to completely solve the problem.
All these examples suggest that the most effective approach to problems of speed and altitude is as follows: power most directly controls speed, pitch most directly controls altitude, precisely what the FAA is saying, and precisely what thefor lack of a better termclassic, more established teaching holds to be untrue.
It is at this point that we can expect the greatest outcry from those who hold to the opposite viewand there are lots of you. I believe the strongest response I have heard to date questioned whether I had just reversed the laws of physics.
In defense of such strong reactions, it is only fair to point out that many of the most energetic come from pilots with experience flying heavy aircraft at low speeds on the approach. There is no question that with low speed and high draga condition properly identified as causing "reverse command"pitch attitude changes become ineffective for managing altitude, leaving power the only remaining effective tool. At the same time, thanks to the high drag, pitch becomes dramatically effective as an airspeed manager: the commands have effectively reversed. Once all this has been said, however, the fact remains that most general aviation pilots fly light aircraft at approach speeds significantly faster than "reverse command." Normal inputs remain the rule.
For a proper analysis of the entire situation, it is essential to identify the precise nature of the issues involved.
"Power plus attitude determine performance"
This phrase, borrowed from "Aerodynamics for Naval Aviators," may not be a word-for-word quote, but is more than sufficiently precise. It tells you everything you need to know to analyze any given flight situation: examine the aircraft attitude, factor in the power being developed and you can predict the resulting performance. The two primary factors, pitch and power, are inseparably linked, and neither can be omitted in an analysis or prediction of flight performance.
It is this twinned nature of pitch and power that renders strident arguments on one side or the other of the pitch/power "controversy" somewhat meaningless. As stated at the start of this piece, after you have been flying for a while you come to the inevitable conclusion that pitch and power affect both speed and altitude; change either, and you will inevitably experience an effect in both areas.
To a very large degree, then, insistence on one or the other of the two alternative approaches to explaining pitch and power is most useful only during initial instruction, when students are in need of useful rules to help in mastering the new dynamics. With increased understanding and experience, pilots learn to predict the effects of pitch and power changes so naturally they give little or no thought to the mechanicsusually making the necessary throttle and elevator inputs simultaneously in order to get the desired result.
This somewhat organic approach works well in VFR flight, where mistakes and results are relatively easy to see and correct. However, whenever there is a premium paid for precision, as in IFR flight, a more scientific approach to pitch and power is worth the effort.
THEORY VS. PRACTICE
In pursuit of precision, it is useful to make a distinction between classroom theory and actual practice. For a classroom example, start with an aircraft in perfectly trimmed level flight and imagine increasing power significantly without making any other change beyond the yaw inputs necessary to remain on a constant heading. The initial reaction should be obviousa speed increase. Over time, because of the increased authority of the elevator trim tab, the aircraft will begin to climb and simultaneously lose its recent increase in speed. Eventually, thanks to the dynamics of increased propeller flow over the trim tab, airspeed will actually stabilize slightly lower than the original level flight value as the aircraft settles into a steady climb.
The exact reverse occurs if the initial change is a power reduction: speed will decrease, the aircraft will start a descent, and speed will eventually settle slightly higher than the original level flight value as the aircraft stabilizes in descending flight.
Both these examples appear to support the "older" teaching points: power seems to control altitude, and, if anything, has the opposite of the expected effect on airspeed.
So much for classroom theory. In practice, this is nonsense: it is unlikely you ever actually start intentional climbs or descents in the manner so described. Much more likely: to start a climb, you raise the nose. For a descent, the opposite. Since both pitch changes have obvious effects on speed, you accompany each with an appropriate power increase or reduction as necessary.
Even more obvious: any attempt to start a missed approach through the simple addition of power without any intentional accompanying nose up pitch change is likely to be suicidal. It simply isnt the right way to fly.
It comes down to this: in making pitch and power changes, you are looking for the most direct path to the desired result. Unless you are at a very high angle of attack, this means you will use power to control speed and pitch to manage altitude. In support of this argument, I will leave you with a final IFR example:
You are on the ILS, glideslope needle perfectly centered, but airspeed 10 knots fast. Assuming you would like to remain on glideslope, how should you start the correction sequence?
Next monthhow pitch and power work with the elevator trim tab.