Airfacts: Attitude Controls Airspeed

- by Niladri Roy

One of the more difficult concepts to grasp in learning to fly light propeller aircraft is that attitude controls airspeed while power controls rate of climb (or descent). The reason why this causes so much confusion among student pilots is that we are so used to the fact that the speed of an automobile increases when we step on the gas. The concept of maintaining the same airspeed but changing only the rate of descent (ROD) by varying power seems totally counterintuitive.

One way to convince ourselves that attitude controls airspeed is experimenting with various attitudes at constant power, and with various power settings at the same attitude. At constant power, it is possible to indefinitely hold, say, 85 knots by holding a particular attitude constant, and equally possible to indefinitely hold 75 knots at a slightly more nose-up attitude. Similarly, by scanning the attitude indicator, airspeed indicator and rate of climb indicator it is possible to confirm that for a particular attitude, different power settings only produce different ROD.

It is important to realize that there will be a period of adjustment after making an attitude or power change before the aircraft settles down. It is perfectly possible that an initial increase in power might result in an initial increase in airspeed (just as lowering the nose will initially result in increased ROD). However, the aircraft will soon settle down to the airspeed determined by its attitude and a ROD determined by its power setting.

Aircraft are designed to be inherently stable. The phenomena described above are no different from the phenomenon of phugoid  oscillations observed when an aircraft flying straight and level is momentarily disturbed nose up or nose down and then the disturbing control input is removed. Phugoid oscillations describe the behavior of the aircraft of oscillating between alternate shallower and shallower nose up and nose down attitudes about a median flight path before settling down to equal the median flight path again.

When NOT to Aim for the Numbers

 - Niladri Roy

We have been taught as student pilots to aim for the numbers while on final for landing.

Aiming for the numbers (or other aim point) is good advice, since it is one way of ensuring we stay on glide slope. However, it is often what we are not explicitly told that becomes the bane of successful execution of a maneuver, whether in flying or other activity. Namely, when is aiming for the numbers no longer a good idea? Knowing when to break off aiming for the numbers can help alleviate the problems many students seem to have in the final moments before touchdown. After flying a consistently stable approach, they still manage to slam the aircraft onto the runway somewhere between the traditional roundout and the flare.

Let us first examine why aiming for the numbers is good advice.

We know, either intuitively or through experience, that a stabilized approach is key to a good landing. A stabilized approach means that the aircraft is:

a.    in the recommended landing configuration – gear down and flaps extended as recommended in the POH

b.    aligned to runway centerline at airspeed recommended in the POH

c.    on the correct glide-slope to the runway

Aiming for the numbers is a mechanism to keep the aircraft on glide slope. Essentially, aiming at a fixed point on the runway means that we do not let that point move up or down in relation to another imaginary fixed point on the aircraft windshield. (Instructors sometimes advise marking a cross on the windshield with a soft pencil and keeping that mark and the aim point aligned at all times).

If the aim point seems to be drifting up on our windshield, we are sinking below the glide slope; if it drifts below, we are rising above. (For the more sharp-eyed readers: Yes, the mere fact that the aim point and the imaginary cross on the windshield are aligned does not mean we are on the correct glide slope. All that the drift can tell us is that we are sinking below or rising above an arbitrary slope. In effect what we really do is that we rely on experience to recognize the runway picture of the glide slope (3, 4 or 5 degrees; power-on approach assumed), acquire that glide slope as our arbitrary slope, and then use the aligning technique to maintain that glide slope).

So why does this seemingly useful technique cause so much grief?

The fault lies not in the technique, but in not knowing when to break out of this rule. Students religiously follow the glide slope almost down to the runway, and then try to execute fairly abrupt roundout and flare by attempting to yank the aircraft level parallel to the ground. This, more often than not, results in abrupt ‘arrivals’ rather than landings as the yanking is invariably too late and the aircraft still carries considerable downward momentum and more or less 'impacts' the ground.

When must one break off aiming for the aiming point?

Aiming for the numbers does not mean that one must almost reach the numbers before one can flare. Keep coming down the glide slope while aiming for the numbers, but, at between 30 and 50 feet above, start pulling gently on the yoke so that the roundout starts very gently and the runway starts leveling out. This will cause your aiming point to drift below the imaginary point on your windshield. This is normal and desirable at this point. Keep practicing this (with your instructor carefully guarding the controls) till you can get to the point where you can fly almost level parallel to the runway and may be 10 to 20 feet from the threshold, while being about 5 feet up. You may elect to cut the power now, or even at an earlier point during the maneuver if you felt you were too high for the "about 5 feet up" to be accomplished at the right time. This will come with judgment developed by practice.

Hold that attitude (do not release control pressure) and look straight ahead at the far end of the runway. It will appear to be not rising or falling with respect to your line of sight. Keep watching and you will see a rise begin (meaning your airplane is dipping). The moment you perceive your airplane begin to dip, smoothly increase elevator pressure (no jerking -- and, BTW, this is flare; the earlier leveling out was the roundout) and continue to increase backpressure (do not ever stop), till the main wheels touch the runway. Then, gently relax backpressure (no abrupt letting go) till the nose wheel touches.

Breaking off from aiming for the numbers is essential to proper roundout and flare – and, consequently, to good landings.

Increasing Safety Margins with Clear Radio Communications

- by Niladri Roy


ATC:         Cessna NXYZ Number 2, cleared to land Runway 25L
NXYZ:      Number 2, cleared to land, NXYZ
ATC:         NXYZ Number 2, cleared to land Runway 25L
NXYZ:      Number 2, cleared to land, Runway 25L, NXYZ

The above exchange took place between Livermore ATC in California and me, in my early days of flight training. My home airport is Palo Alto, California, which has a single strip of concrete: Runways 31 and 13. Naturally, when issuing a landing clearances, all that ATC would say was ‘NXYZ [Number n], cleared to land’, since there was only one active runway at any time. When I started to venture out of Palo Alto to nearby Livermore, however, the situation was quite different. Livermore has two parallel runways, 7/25L and 7/25R, and it was necessary to acknowledge not only the landing clearance, but also the runway that the clearance had been issued for. As is evident from my exchange with Livermore ATC, I had omitted to include the designated runway during my first acknowledgment.

It’s not that I was not aware that I was required to acknowledge the runway I was cleared for. It simply had been too much of a force of habit at Palo Alto to just acknowledge ‘[Number n], cleared to land, NXYZ’.

This got me thinking about the necessity of cultivating a habit of clarity in communication with ATC. Nowadays, even at Palo Alto, I always mention the runway number, even though it isn’t strictly necessary. Examples include:

ATC:         Cessna NXYZ, pull up and hold short
NXYZ:      Hold short, Runway 31, NXYZ

ATC:         Cessna NXYZ, Position and hold
NXYZ:      Position and hold, Runway 31, NXYZ

ATC:         Cessna NXYZ, Runway 31, cleared for takeoff.
NXYZ:      Rolling, Runway 31, NXYZ

ATC:         Cessna NXYZ [Number n], cleared to land
NXYZ:      [Number n], cleared to land, Runway 31, NXYZ

Sure, as a pilot one needs to maintain situational awareness (and that includes knowing if there is one runway or multiple) and needs to be crisp and clear in communication with ATC without using up any more of the frequency than is necessary, but I find that cultivating the habit of mentioning the runway number in the above exchanges, even when the designated runway is obvious, helps me in getting it ingrained into my system, so that I never forget to mention the number at airports where it is, indeed, necessary to mention it. It takes very little extra time and effort and makes one a safer pilot. One need only consider a non-towered airport with multiple -- and, to keep things interesting – intersecting runways, where multiple pilots may choose the same or different runway at will, whatever their reason may be, at the same time, to see the benefits of developing a habit of clarity.

Non-towered airports can benefit from clarity in pilot communication over the CTAF beyond just calling out runway numbers. How often, for instance, has one heard ‘Smallville traffic, NXYZ, is turning base for Runway nn, Smallville traffic’ and wondered, “Gee, it sure would be nice to know if the pilot meant left or right base” and whether it was a Citabria which is a lot slower than one’s Cessna, or a Bonanza that is chewing up the air fast enough to be on one’s tail before one could say Evasive Maneuvers.

Sure, there are published traffic patterns for non-towered airports, but if, like me, you have, while on right base, seen a Piper Cub come streaking in for a straight-in approach at Half Moon Bay, CA (where straight-in approaches are specifically prohibited), you sure would be grateful for small mercies in communications.

Here are my other rules of thumb on the clarity in communications theme that I have developed for myself for non-towered airports:

1.    On the ground, I never say I am “taking the active”. My preferred transmission is to always include the runway number

2.    In the pattern I never say “… is on downwind for Runway nn”. It’s always “…left [or right] downwind for Runway nn”

3.    If I am turning final behind another aircraft, it’s never “… is on final for Runway nn” It’s always “… is on final for Runway nn behind the [Cessna, Piper, Citabria, etc.]”. Not only is it good for the peace of mind of the pilot ahead of me, chances are, knowing that there is an aircraft behind, the plane will not dally on the runway but will expedite an exit.

4.    Finally, I never give only my call sign. It’s always preceded with “Cessna [or Skyhawk]…” The other person looking out for you cannot read your tail number from wherever they are, but have a better chance of finding you (and not confusing you with someone else) if they know what they are looking for. Additionally, it is useful for them to know whether you are a slower or faster aircraft than them so that they can adjust their pattern accordingly, or if an impending emergency is suspected, get out of the way.

Practicing clarity in radio communications, even at the expense of sometimes stating the obvious, develops habits that can contribute to increased flight safety, in the air and on the ground.