Two pilots dressed for a fancy-dress party, in a cow-suit .. or .. What controls what, on final?
Two pilots dressed for a fancy-dress party, in a cow-suit .. or .. What controls what, on final?
Do you know why some pilots still try to fly a POWERED final approach using the SECONDARY effects of the PRIMARY flight controls?
Neither do we!
We shall discuss glide approaches, later in this article. But arguing about what controls what, on a final approach – when variable power or thrust is available – has occupied far too much time and confused far too many pilots, for over 100 years. It is vital to the understanding of HOW to aim the approach, accurately, yet the argument still rages. It shouldn’t.
Let me conceive a comical image: Imagine how ridiculous-looking, ungainly and haphazard would be the sight of two pilots heading out to a fancy-dress party, dressed in a COW SUIT.
The guy in the front would, presumably, be responsible for finding their way to the venue and steering the ‘beast’, while the poor individual providing the hindquarters would essentially maintain a stooped-over profile and act as the limiting factor on their speed, neither pushing too hard, nor allowing the front half to drag him/her along, too fast.
Now, please hold these thoughts, for a minute or two.
On a normal, powered, manually-flown approach, the pilot’s flying hand – the one holding the control column – is maintaining both the extended runway centreline and the consistent 3º approach path angle, just like finding the party in the above scenario; the hand on the throttle maintains the selected approach speed and, together with the brain of the pilot, the complete approach is coordinated. It is instructive, also, to consider how an ‘artificially-flown’ approach is constructed.
In an airliner, conducting a ‘coupled instrument approach’, the autopilot and autothrottle systems perform the same functions, respectively, yet quite independently from each other, using only the primary effects of controls. It is the automated flight control system (AFCS) that coordinates the inputs to control both the approach path and airspeed and simulates the manually-flown approach with impeccable accuracy and stability.
Moreover, because the aircraft is not pitching up and down, the stability of this ‘PATH’ descent also facilitates the application of the unique Jacobson Flare visual fix. It is an accurate, far straighter flight path than the ‘conventional roller’ coaster path of varying amplitude and runway threshold crossing heights, resulting from pitching to maintain approach airspeed. A handy side-effect is enhanced passenger comfort, especially in large aircraft with inherently great inertia and a limited supply of airsickness bags!
The stability of this PATH descent also facilitates the application of the unique Jacobson Flare visual fix: No roller coaster path, here.
There are two occasions, however, when it is appropriate to control airspeed with the SECONDARY effects of the elevators:
On take-off and in the subsequent climb, for example, with take-off power or climb power set, the pilot must utilise the elevators to control the airspeed. There is no alternative.
The second occasion is on approach, IF the power output is constant (or failed, partially or completely). It is necessary, then, to control airspeed with the elevators (along with refining the approach path angle, through judicious tracking and deployment of landing flaps). This is generally a training manoeuvre, such as when practising a NON-NORMAL procedure, such as a forced landing. It is a compromise – inaccurate and results in an oscillating, inconsistent, ‘rollercoaster’ path.
Now, why would anyone want to apply the secondary effects of controls, rather than the primary effects, IF THEY DIDN’T HAVE TO, when flying the most precise manoeuvre that most pilots ever need to master? Not to mention making so many corrections of corrections. Absolutely NOTHING remains stable: Not the power setting, the elevator inputs, the path angle, airspeed, vertical speed or aircraft trim.
Sailplanes (gliders) are normally flown this way; for without power, these aircraft are always descending through a parcel of air which, hopefully, is itself rising faster than the actual descent rate of the sailplane within it (that is, a thermal).
However, most approaches and landings are flown in powered airplanes, where the power output is variable and reliable: Therefore, the afore-mentioned PRIMARY effects of the controls should be applied: The constant approach path angle is maintained with the elevators, by aiming the pilot’s eyes at a suitable aim point and the throttle is utilised to vary the power, slightly, to maintain the selected approach airspeed (IAS) through each flap configuration and wind change.
This is not new to generations of military and airline pilots, but seems to meet ignorant and stubborn resistance, by some misinformed general aviation (GA) flight instructors and their unsuspecting students. The costs are immense, in terms of time, cost, pilot stress and aircraft damage. Many instructors insist that airspeed is controlled with the elevators and the vertical rate of descent is controlled with power; this is misconceived. The use of an increase in power certainly does facilitate descent flight at a reduced path angle, for a given airspeed): However, it is the reduced path angle that reduces the rate of descent, not the power. This particular point has been long-lost in the translation, over the last 100 years.
The rate of descent on an approach is the result of two variables: the flight path angle and the aircraft’s ground speed.
OK, let’s return to where we started: Two pilots dressed for a fancy-dress party, in a cow-suit …
From the foregoing, it should become clear that flying a NORMAL, powered approach with a ‘SPEED’ descent, that is, with the secondary effect of the elevators controlling airspeed and power supposedly controlling the rate of descent/path angle, is just as silly as having the guy in the front of the cow-suit, who can see where to steer, worrying only about how fast they are going; and the guy down the back, who cannot see a damn thing, trying to find the party.
So, the comical cow-suit analogy is quite relevant.
There are many more advantages in flying an accurate ‘PATH’ descent: To learn more on this, please review FAQ #5, in https://www.jacobsonflare.com/our-most-frequently-asked-landing-questions/ . The Jacobson Flare App, of course, expands at length, also, on this critical aspect.
Captain David M Jacobson
Wishing you many safe landings
Captain David M Jacobson FRAeS MAP
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