Back in 2016, the FAA did something that made a lot of sense but didn’t get a lot of attention. Its Policy Statement regarding Approval of Non-Required Safety Enhancing Equipment (NORSEE) provided guidance and procedures for issuing design and production approval to a U.S. manufacturer that is determined to be a minor change to type design and whose failure condition is minor.
The purpose of NORSEE is to encourage voluntary installation of safety enhancing equipment without the need of an STC—as only a minor modification of an aircraft—minimizing paperwork for an owner and a shop. In December 2025 the FAA went a step further by issuing a Special Airworthiness Information Bulletin (SAIB: 2024-07) to outline the benefits of installing angle of attack alerting systems in reducing the risk for loss of control accidents.
We’ve been fans of angle of attack indicating and alerting systems ever since an unpleasantly wild ride following an inadvertent accelerated stall in an airplane with very light pitch control forces. We’ve also noted that most all military flight operations make the angle of attack indicator the primary pitch instrument on takeoff and landing.
For this field report, we reviewed the Absolute AoA system that was brought to market last November by Holy Micro, a Syracuse, New York-based avionics safety equipment manufacturer. The system was approved by the FAA under NORSEE in June 2025. Our installation is in a STOL- and VG-equipped Cessna 182J Skylane.
Beyond the Airspeed Indicator
Put simply, the airspeed indicator is not a great indicator of what the wing is doing when flying at other than 1 G, as is common in turns and maneuvering, which means that there have been many fatal loss of control stall accidents that might have been prevented with an AoA system in the airplane. We also like AoA indicators because they make it clear when the wing is flying again during stall recovery and can help minimize altitude loss in the recovery, which may mean the difference of climbing away with a system-load of adrenaline instead of diving into the ground when trying to make sure that there won’t be a secondary stall during recovery.
AoA indicators are also a big help when dealing with low aircraft energy situations such as a go-around, clearing obstructions after takeoff, and hazardous conditions such as wind shear or maneuvering to avoid terrain, and allow the pilot to take advantage of maximum wing performance near stall AoA. We also would have liked to have an AoA indicator for landing in an airplane in an event when we took a bug into the pitot tube during flight and when some water in the static system froze while parked overnight—both cases rendering the airspeed indicator inoperative during flight.
The Absolute AoA system developed by Holy Micro is described as using a normalized pressure ratio with multiple sensors to allow accurate AoA indications regardless of density altitude, loading conditions or flap settings. The company says that unlike traditional single-sensor differential pressure systems that are limited to near stall warning, this system provides reliable AoA information for climbing, cruising, and landing, unaffected by density altitude or weight/loading. In addition, the underwing probe that is the external portion of the system has a “flap scanner” that uses LiDAR (Light Detection and Ranging) to detect and adjust the system for position of the flaps. That’s the AoA probe, sensor, and wiring pictured here.
Currently priced at $2,650 (with a one-year warranty), the system includes the sensor unit, which is installed in the wing near the probe and connected to it with color-coded tubes; the underwing probe; a CPU (central processing unit) box; an HMI (Human Machine Interface—an Android smartphone); and a display unit (touch capable), with a choice of a panel- or glare shield-mounted display. Since the system weighs less than a pound, no change to the airplane’s weight and balance paperwork is necessary.
Installing It
The company provides a massive amount of detailed information on the AoA system via manuals accessed through its website and several videos describing the process of installing, calibrating, and using the system. Holy Micro advertises that installation can be done in an hour. We couldn’t even get through all of the written or video material in an hour, so we assume the company is referring to a shop that has done at least one installation previously and is only making the most basic installation where the system audio comes through a battery-powered Bluetooth speaker and the flap position sensing is not calibrated on the ground.
The shop that did our installation, Northern Air Aeromotive on the Boundary County Idaho Airport, took slightly over 10 hours. A significant part of that installation time was because the STOL kit on the Cessna 182 used for the review had an upward camber on the portion of the lower wing aft of the leading-edge cuff (the probe was mounted on an inspection plate) that pointed the probe too far forward, and focused the LiDAR flap-sensing system below the wing flaps. Holy Micro provides a set of shims with the kit so the probe can be accurately positioned; however, none were of the size necessary for this installation. From a series of telephone conversations with Holy Micro, A&P/IA Phil Heisey developed a mount that allowed the probe to “see” the flaps. Heisey told us that Holy Micro always responded quickly to questions and were able to provide needed information. He rated the customer service highly.
The Holy Micro Absolute AoA system begins with the underwing probe that has four pressure ports. Two capture ram pressure from the airflow; the other two ports, angled 45° aft, capture the static pressure. The pressures are transmitted via hoses to the sensor unit mounted in the wing near the probe. The sensor converts the pressure data into digital signals that are communicated to the processing unit (CPU) located behind the instrument panel. The CPU communicates with the display unit to present AoA indications which may be presented in a number of formats, based on pilot preference. Two types of auditory warnings (pilot selected) are transmitted to the headsets or a battery-powered speaker.
The HMI unit is an Android smartphone with the Holy Micro app installed. The app can be downloaded to virtually any smartphone or tablet. The app includes a series of videos on installation, calibration, and use of the AoA system. It also receives updates that are sent out by Holy Micro for the life of the product. The HMI is the primary method of communication between the pilot and system, first for system calibration and then for the pilot’s selection of display and audio options. No internet connection is required for the HMI to talk to the CPU as they communicate via Wi-Fi.
Critical Calibration
Once installed and ground tested, calibration of the system in flight is not complicated but should be done in relatively smooth air by a pilot who can precisely hold altitude when making speed changes and make those changes at a rate of about one knot per second. We found that it worked best to have two people aboard, one to concentrate on flying the airplane and the other to use the HMI for the needed calibration runs.
Before flight, information on the airplane is entered into the HMI. It then generates the Carson Speed—the speed that is the optimum balance between the desire for fuel efficiency versus the desire for speed. It’s about 32% above the best lift over drag speed. It serves as the baseline for calibrating the system. Calibration consists of first climbing to the altitude called for by the HMI after you click the “AoA Calibration in the Air” button on the HMI touchscreen. Once at altitude, you fly level for the barometer calibration. Push “calibrate,” and the system makes its barometric calibration. After that come IAS calibration—slow to the Carson speed for the airplane and click “calibrate.” The HMI will display the IAS measured by the AoA system. It should match the IAS on the airplane’s airspeed indicator.
The final steps are to make calibration runs with the flaps up and in as many as three deflected positions after climbing to a safe altitude. Each run starts at the Carson speed. Once stabilized, the “start” button is pushed, and the pilot holds altitude while slowing the aircraft at about one knot per second (the HMI pops up a graphic depiction of the rate the airplane is decelerating, with a green band showing the ideal rate)—although the system has some margin for error.
As soon as the stall warning sounds, the “stop” button is pushed (the pilot noses down and applies power) and the system tells you whether the calibration was successful or not. Once the flaps up calibration is successful, the system walks you through the same deceleration procedure for three different flap positions.
That’s it—once the system confirms that all for calibration runs were successful, the AoA system is ready to go.
The Displays
Each of the AoA displays are color-coded and the indicator moves upward as the angle of attack increases. Green means the Carson cruise speed, yellow is best glide, blue is best approach, and red warns that you are near the stall. In addition, there is a digital indicator that shows lift review as a percentage—the number drops as the stall is approached so a pilot has a precise indication of the margin above stall. Each display also shows flap deflection from zero (F0) to full (F3).
For the dash (glare shield) mounted display, there are three presentations from which to select. The chevron presentation (think sergeant stripes) has 13 segments with each corresponding to a specific angle of attack from Carson cruise to stall. The bar display has 19 horizontal segments that graphically show the wing’s progression to higher angles of attack starting at Carson speed. The performance presentation also has 19 segments but presents angle of attack in a slightly different fashion. The donut in the middle of the display is the reference point; it is flanked by two vertical tapes with color-coded angle of attack on the right and indicated airspeed on the left. The performance presentation is the only one that allows user-set reference points such Vx and Vy to be displayed.
The panel mount display adds one additional form of AoA indication—a sweep needle. It has 13 segments presented in a curve on the left side of the display and a needle hinged on the right side moving to point at the appropriate location on the curve.
For our review we installed the glare shield-mounted display, so we did not have a sweep needle. However, in looking at the installation manual for Absolute AoA, the sweep needle appears to be similar to the AoA indication in other applications, including the Icon A5 seaplane we’ve flown, which we found very easy to interpret with minimal practice.
Audio Alerts
There is a switch to turn the audio alerting system on or off. The HMI is used to select either voice “getting slow” and “too slow,” or the Air Force/Navy standard 400 Hz intermittent tone (best glide), solid 400 Hz tone (best approach), and 1600 Hz tone for approaching stall. Even after several flights, we’re not sure which we prefer. We also found that it’s not uncommon for either audio to briefly say something or beep (depending on which alert mode is selected) when taxiing out. It’s a little strange to hear it say, “Getting slow,” for the first time when taxiing. We found ourselves turning the audio off so as not to disconcert passengers when on the ground. That raises the problem of forgetting to turn it on before takeoff.
Flying It
In our installation the AoA system boots up and displays when the avionics master is turned on. If it’s desired to use the HMI to make a change to the display, it can be turned on at any time and will automatically link with the CPU. After liftoff, the AoA indicates in the red for an angle of attack near stall speed—and shows a low percentage of lift reserve. A good reminder that the airplane is in a low-energy state that needs to be respected, especially on a high density altitude day. As speed builds in the climb the indicator moves out of the red zone, through blue and into yellow or green depending on the selected climb speed as the percentage of lift reserve increases fairly rapidly. In cruising flight no bars are illuminated.
We experimented with holding best glide speed, keeping the indicator in the yellow in level flight and in steep turns. We like that it when we reefed the airplane around in a steep bank, simulating an attempt to make “the impossible turn” after takeoff while holding the published best glide speed, we got an audio and visual warning that we were flirting with an accelerated stall and pitched down slightly to remedy the situation.
Setting up a full-flap approach when lightly loaded we found that holding the blue segment was challenging. The system is sensitive but not twitchy. At that weight we also noted that the indicated airspeed generated was well below the speed we normally fly on final when fully loaded. When doing stalls clean and with flaps extended the Absolute AoA gave us plenty of warning that our lift reserve account was approaching exhaustion. During stall recoveries it didn’t take much effort to learn how far we needed to lower the nose as we added power and the earliest time that we could pull up and start to climb to minimize altitude loss. We didn’t check carefully, but our impression was that we lost on the order of 200 feet less in a stall recovery with the AoA information than without.
We had selected the on-the-dash display because we wanted the presentation up where we could see it without having to look down at the instrument panel. Now that we’ve used it for a while and have used panel-mounted systems, we are glad that we chose the dash mount.
As to our preference for display presentation, we initially thought that the chevron was going to be the one, but as we used the system we found ourselves preferring the either the bar or performance display. That will probably change as we get more experience. We also can’t decide whether we like the voice or tone alerts; however, we have our discomfort with the voice alerts when carrying passengers who might misinterpret them.
Our Conclusions
In our opinion, Absolute AoA from Holy Micro is an incredibly feature-rich system that provides accurate and safe stall warning in all flight conditions (except icing) and aircraft attitudes, plus providing information valuable to the pilot in all aspects of flight.
Holy Micro provides a boatload of information with its Absolute AoA kit. We spent a few hours working our way through it as we kept finding new features and wanted to make sure we understood them. The written and video materials were, in our opinion, prepared by engineers who understand aerodynamics and were determined to provide as much useful information to pilots as possible.
If we’re going into the backcountry, have to maneuver or deal with the stress of an engine-out glide, we want an angle of attack alerting system that is easy to see and interpret—and we like the one from Holy Micro. We’ll look at other AoA systems, including the redesigned Alpha Systems AOA, in an upcoming report in Smart Aviator.