“Keep the dirty side down. Airspeed is life. Rudder in the turn.” – Captain Blackcloud
Aviation tends toward pithy, easily remembered sayings for complex subjects. The quote above is a good example. These cogent reminders would not be repeated as often as they are unless absolutely true – and worth knowing. Of all the things you need to remember in aviation, a laser-like focus on airspeed should be at the very top of the list. Without airspeed, your aircraft will not stay in the air.
At AirVenture Oshkosh in July 2024, there was a stall/spin accident in the traffic pattern for Runway 36L with two fatalities. A Lancair ES got low and slow while maneuvering for a left base to final turn. The combination of decelerating airspeed, minimal altitude, and a sharp turn toward the runway centerline appear to be factors. Conditions were Day VFR and heavy traffic pattern congestion. We will leave it to the NTSB to determine probable cause and to the litigators to argue legal fault.
Clearly, as PIC, you have an obligation to monitor and maintain airspeed and keep your aircraft flying. If you become task-saturated or distracted, and you lose sight of your airspeed even for a moment, close proximity to the ground on a base-to-final turn will leave you no time to recover from a stall. Your concentration level should be at its highest when you are at a low altitude.
Airspeed matters.
There is a means to improve awareness of airspeed in the pattern. In the GA world, this has not received as much attention as it should. I have been flying for over 30 years, and I only became aware of it a few years ago.
During private pilot training, advanced training, and when transitioning to a new aircraft, there is an emphasis placed on airspeeds or “V-speeds.” Every student pilot and certificated pilot should commit to memory the V-speeds for his or her aircraft. These include takeoff speed (VR or V1 and V2), flap and gear retraction and extension speed (V3, VFE and VLE), best angle and best rate of climb speed (VX and Vy), maximum structural cruising speed (VNO), stall speed (VS1 and VSO), and never exceed speed (VNE). These normal “book” V-speeds are what you are asked to memorize and concentrate on.
However, airline pilots and other professional pilots recognize and employ an additional V-speed. This is Defined Minimum Maneuvering Speed (VDMMS). Dan Gryder, a retired Delta pilot, Gold Seal flight instructor, and popular host of “Probable Cause” on YouTube explains, “The big missing element here is that we have not been proclaiming avoidance as a first step, we’ve been teaching . . . stall recovery techniques . . . and how to get out of a spin . . . .” See “Podcast: Dan Gryder Tries a New Take on Stall Avoidance,” AvWeb/Aviation News, September 29, 2019.
The airlines realized long ago that they did not want their pilots flying anywhere close to a stall. Airline training emphasizes stall avoidance, not stall recovery, through VDMMS. It is calculated as a referenced V-speed for every flight. GA pilots can and should be doing the same thing.
VDMMS is arrived at as follows: 1.404 times VS1 (“clean” stall speed or minimum steady flight speed for which the aircraft is still controllable in a specific configuration for your aircraft), i.e., the top of the green arc (lowest green arc speed) on your airspeed indicator (“ASI”). This equation allows a minimum 30 percent buffer above stall speed and then adds another eight percent buffer to account for a 30-degree angle of bank. For example, 1.404 x 50 kts VS1 = 70.2 kts VDMMS.
VDMMS should be used when flying in the traffic pattern, turning base-to-final, and on final approach (until the approach is stabilized on short final and the landing is assured). Knowing the VDMMS provides a quick and ready reference minimum speed and, if adhered to, is measured to prevent you from stalling your aircraft. It is also useful as a close approximation of initial climb speed in a go-around scenario and best glide speed in an engine out scenario (single engine).
GA over the years has suffered far too many fatalities from flying at too slow an airspeed during a base-to-final turn, or when conducting a go-around, or when attempting to maneuver and land during an engine out emergency. The tragic consequence of failing to pay attention to airspeed in stressful or rushed situations and allowing airspeed to drop below VDMMS, is often an unrecoverable stall/spin accident.
However, VDMMS is not depicted on the ASI. You can attempt to remember VDMMS for your aircraft and visualize that V-speed in relation to the needle on your ASI. It can be done, as it would not be much different than visualizing other V-speeds along the circumference of the ASI, such as VNO in relation to the needle. But why attempt to visualize when you can mark VDMMS on the ASI instead? When a pilot is stressed or distracted, the easier it is to quickly identify the calculated VDMMS on the ASI, the better the chance to prevent airspeed from dropping dangerously close to or below it.
It is easy to position a “bug” or add a “marker line” to the ASI to reference VDMMS. If you do not have a bug that you can rotate to the VDMMS on the bezel of your ASI, you can create a marker line out of a thin piece of adhesive tape, preferably a bright, high-visibility color like red, orange, or yellow, and place that on the face of the ASI. You will then have a visual, easy-to-see cue when you are getting close to your VDMMS. For glass panels such as Garmin’s G1000 all-glass avionics suite that displays an airspeed tape on a screen, the capability exists to add any calculated V-speed and mark it with an electronic bug on the airspeed tape. You may need to delve a few screens into the menu to accomplish this, but I understand the airspeed display can be so configured.
Once you have identified and marked VDMMS for your ASI, use it. VDMMS should become your minimum speed target in the traffic pattern, on a base-to-final turn, and on final. Your airspeed should never fall below VDMMS. With a bug or marker line, you should always be able to quickly reference your indicated airspeed in relation to VDMMS.
When flying with friends or family, as you enter the traffic pattern is often the moment they choose to ask questions about the airplane, ask you to comment on some landmark on the ground that catches their attention, or ask you how to adjust the fresh air vents. At the same time, you may be looking for traffic, listening for or talking to traffic, or trying to process what an air traffic controller is telling you. You may be managing prop, mixture, throttle, flaps, gear, and going through your landing checklist. We have all been there. Stress. High workload. Multi-tasking. Distractions.
This is when you need to focus on VDMMS. To assist you, one easy thing you can do is also borrowed from the airlines. In 1981, the airlines started the standard operating procedure (“S
OP”) of maintaining a “sterile flight deck.” This SOP is designed to inhibit any unnecessary actions or conversations during critical phases of flight, i.e., usually defined as taxi, takeoff, approach, and landing.
You can increase your chances to remain focused on VDMMS if you eliminate as many unnecessary distractions as you can. Prior to any flight with passengers, politely advise them that it is your intention to maintain a quiet cockpit at certain times. As part of your preflight brief, in addition to explaining use of seat belts, egress procedures, and where the sick sacks are located, also explain the “ground rules” on passengers talking with or creating unintentional distractions for the pilot. This is helpful for the passengers and can make life much easier for the pilot. Of course, if everyone is wearing a headset, as the pilot you may have the option of isolating the intercom, thereby creating the required silence. As a courtesy, you may want to let your passengers know when you intend to do that.
Sometimes, however, you simply cannot avoid a high workload or distractions while flying in the pattern. Your attention is directed momentarily forward to the horizon, then to the right, and then to the left, as you scan for traffic and locate where you are in relation to the runway. Your eyes then quickly dart to the panel. Outside, then inside, then back outside – rapidly and repeatedly. Mix in some difficult-to-locate traffic with you in the pattern, add a few radio communications, and the amount of time you can devote to any one task may only last a second or two. A short peek at the ASI may or may not be possible or sufficient, particularly if your attention is demanded elsewhere. But, if you have a bug or marker line denoting VDMMS, you may only need a quick glance, because now you can easily see where your airspeed needle is in relation to your minimum reference speed.
An Angle of Attack (AOA) indicator also is a great visual cue for flying in the pattern. Naval aviators and Air Force pilots rely, in part, on AOA to fly more precisely for approach and landing. The retail prices for AOAs are not unaffordable, but most of GA still does not use them. A bug or marker line denoting VDMMS remains relatively inexpensive in comparison.
The choice to use VDMMS as a minimum reference speed is entirely yours. Some pilots may ask “What do I need VDMMS for?” Instead of glancing constantly at the ASI, they operate in the pattern mostly looking out the windshield, flying sight pictures of the horizon on downwind, base, and final, and setting pitch and power for a desired speed and descent rate, paying scant attention to the ASI. They may know the feel of an impending stall in their aircraft and use that as the initial wake-up nudge to lower the nose and increase airspeed. They may say “I always fly the recommended speeds” for the aircraft and configuration on downwind, base, and final.
That is fine – if they can do it every single time – and do it precisely – despite varied bank angles, distractions, or momentary lapses in concentration. I would rather have an early visual alert.
Other pilots may say “You cannot fly VDMMS on final.” That is partly true. Once you are stabilized on final, continue to fly your aircraft and configuration-appropriate reference speed. If you don’t fly below VDMMS on short final, obviously, you will have trouble, as you will probably be too fast over the runway numbers.
We have been trained repeatedly to recognize impending stalls and how to recover from stalls. For years the FAA’s Practical Test Standards (PTS), now the Airmen Certification Standards (ACS), for slow flight and stalls required applicants and pilots to identify imminent stall characteristics, bring their aircraft to the edge of a stall or just over the edge, and then to recover. It is good experience and a vital skill to possess, but what we really should be directing our training toward is avoidance. We do not want our airspeed to go anywhere near stalling our aircraft. Our margin of safety is dramatically increased if we can recognize when we are close to our aircraft’s VDMMS – and react appropriately at that point.
I think you would agree; avoiding a stall close to the ground is always preferable to attempting to recover from one.
DISCLAIMER: The information contained in this column is the expressed opinion of the author only, and readers are advised to seek the advice of their personal flight instructor and others, and refer to the Federal Aviation Regulations, FAA Aeronautical Information Manual, and instructional materials before attempting any procedures discussed herein.
© Copyright Dean Zakos 2024. All Rights Reserved!
