Angle of Attack (AOA)

Angle of Attack (AOA)


You are hand-flying an in-the-weather descent, power back, heading for the FAF. You start a 30 degree banked turn at your lead point to cross the FAF, when your passenger behind you gasps. Looking over your shoulder, you see he has spilled his drink into his lap…too bad for him! However, when you turn your head back to your panel, your inner ear tumbles and you see 45 degrees of bank, 15 degrees nose low, airspeed increasing.

Congratulations! You have managed to get distracted and sucked into an unusual attitude recovery. By the book, you should roll wings level, pull to the horizon, and adjust power as necessary to keep the airspeed within limits. In this scenario, if you had not experienced vertigo, you might have been able to roll to less than 30 degrees of bank, recover your turn, pull the nose up to less than the original descent attitude, pulled a bit of power to slow back to your desired penetration speed and then resumed your desired ground track. However, this would only be appropriate if you had full situational awareness as to the deviations caused by the look over your shoulder, plus full confidence that the moderate corrective actions would put you back on your desired flight path.

As a military aviator, I learned unusual attitude recoveries based upon hard maneuvering at extreme pitch and bank angles. In the hard-maneuvering environment, an unusual attitude could be 90 degrees straight up, airspeed decreasing below 120 kts…or 80 degrees nose low, 135 degrees of bank, airspeed increasing through 500 kts… etc. In these cases, understanding angle of attack, or AOA, is critical to maintaining controlled flight and returning to a normal attitude.

In an extreme nose-high attitude, a military aviator is trained to roll the aircraft to 90 degrees of bank, ease off the back-stick pressure to reduce AOA, add power as required, and allow the nose to slice back towards level, rolling to wings level as the nose approaches the horizon. If nose low, the recovery procedure is to roll rapidly, within asymmetric g limits, until wings level, then to pull at optimum g loading to recover to level flight. For the nose-low recovery, power was normally reduced until airspeed could be assessed and brought under control. However, when doing the nose-low pullout at 7-9 gs, pulling the power for too long would leave you much to slow to resume combat.

The AOA gauge on a fighter’s glare shield is a primary reference during hard maneuvering and for landing. The AOA for optimum maneuvering is 13 degrees, displayed as the green circle or “green donut” on the gauge. The red chevron on top represents a slow condition of 15 degrees or more and the yellow lower chevron represents 11 degrees or less.

For normal landing in the F-16C, the pilot slows to 220 kts and configures abeam the touchdown point while mentally computing the final approach airspeed of 136 kts plus 4 additional knots for each 1000 lbs of fuel. When rolling off the perch and flying the final turn, the pilot would usually only glance once at the airspeed once to ensure final turn airspeed of 180 kts while using the AOA sight gauge as the primary indicator of a best performance turn. As long as the AOA was green donut (13 degrees) or less, you would not stall. If on speed and 13 degrees wasn’t going to get you around the turn to line up with the runway, you knew you were going to overshoot. You never wanted to see the red chevron of 15 degrees or more as that meant you were too slow, pulling too hard, and in danger of building an un-recoverable sink rate!

Few GA aircraft are currently equipped with AOA indicators, though there are several after market devices available for retrofit. However, knowing the impact of AOA and how to manage it is vital to safe aviating, even without an AOA gauge. The bottom line is, as long as you don’t ask the wing to produce more angle of attack than it can handle, you won’t stall.

Practicing final turn stalls, to know what the wing feels like as you get too slow or pull too much on the controls, increasing AOA past the critical point, will keep you safe when you encounter that unexpected overshooting wind or you find yourself inadvertently on too tight of a downwind leg. Better to overshoot or take it around to try again, than to pull too hard and exceed critical AOA.

Mike Hostage is a retired USAF pilot with 37 years of experience, flying a wide variety of aircraft.  An instructor pilot for more than half of his 4800 flight hours, Mike is currently qualified in a Cirrus SR-22T and regularly flies his two homebuilt sailplanes.

Wind the Clock


There is truth in the old adage that 99% of flying is routine while the remaining 1% holds the potential for events that cause those who fly to hold themselves above mere ground-bound mortals. My 37 years of military flying might have distorted that ratio a fair bit given the complexity of high-energy fighter aircraft and the uncertainties of combat, but rest assured we all earn our right to be proud of our wings every time we fly.

The requirement that a single-seat fighter pilot be able to handle rapidly evolving emergency situations and complex systems diagnosis sets a high bar for any who join that group. However, the lessons we learned and techniques we developed for making fighter aviation significantly safer than in yesteryear have direct applicability to general aviation.

Prioritization and compartmentalization are two important skills that every pilot should have. These skills amount to the ability to look at a complex problem, quickly determine the most critical elements, and mentally set aside those things that can wait so as to deal with highest priorities first. While this does not sound like rocket science, the art is in the doing!

The technique for dealing with the immediate onslaught of information, such as when that caution tone or caution light presents and different gauges or displays go haywire, provided the title for this piece.

All flight training will, at some point, involve what is called situational emergency procedures training, know to military aviators as SEPT. We do this type of training in a simulated cockpit that has all the dials and switches for our particular aircraft. None of the switches and dials do anything, some are just decals on a wooden dashboard, but the presentation allows the SEPT victim to reach for the appropriate switch or lever, while telling the instructor what and why they are doing so.

One of the most common mistakes new trainees make is that of trying to act too fast, before they have fully and correctly analyzed the situation at hand. Herein lies the titled technique. After blurting out a quick and incorrect answer, the instructor would admonish with: “rather than try to react instantly, maintain aircraft control, analyze the situation, then take appropriate action. The best thing you can do is to reach up and wind the clock. This will give your nervous energy some place to channel itself, while your brain takes in the full situation.”

Waltham clock

Winding the clock might seem like an archaic notion, but, amazingly enough, even our most modern aircraft have the same clock we flew with as far back as the 1960s. The Waltham A-13A aircraft clock and timer is a wind-up device that only uses power to light up at night. Unless your emergency involved some type of catastrophic impact to the instrument panel, you could count on at least your clock to be functioning normally. Thus, reaching out and winding it was unlikely to cause any worsening of your evolving emergency and would distract your brain from the need to take some poorly-thought-out action, too quickly.

Now, in most aircraft there are a few emergencies that will require immediate, reactive actions. In fighters, we call these Boldface Emergencies. For each type of fighter, we memorize, to the letter, the few key actions that have to be instinctive, to prevent disaster. For all other emergencies, there is time to reach out and wind the clock while assessing all instruments and lights to fully understand your situation.

For your aircraft, know those Boldface or Critical Action Procedures, but for all other emergencies, take the time to maintain aircraft control, “wind the clock” while you analyze the situation, then take appropriate action.

Mike Hostage is a retired USAF pilot with 37 years of experience, flying a wide variety of aircraft.  An instructor pilot for more than half of his 4800 flight hours, Mike is currently qualified in a Cirrus SR-22T and regularly flys his two homebuilt sailplanes.