OnSpeed AoA

ATA Chapter 34 — N720AK Systems Reference

Overview

The OnSpeed system is an audio angle-of-attack (AoA) indicator that provides continuous tone-based feedback on the aircraft’s energy state. It uses differential pressure from the pitot-static system to compute AoA and delivers audio tones through the intercom.

Components

Component	Part Number	Supplier	Notes
OnSpeed box		FlyOnSpeed	Main processor
Pressure sensors

How It Works

OnSpeed converts AoA into a continuous audio cue. As the wing approaches stall, AoA rises and the tone changes to give the pilot a head-out-of-the-cockpit indication of energy state and stall margin. The tones are the primary reference; the percent indicator on the panel is descriptive after-the-fact information, not directive.

Tones — What They Mean

As you slow down (AoA increases), you progress through five regions:

 FAST ─────── L/Dmax ────── ONSPEED ────── SLOW ─────── STALL
 (silence)   (low-pitch    (ONSPEED       (high-pitch   (stall warning
              pulsing)      solid tone)     pulsing)      buzz)

Region	Tone	Meaning	Pilot Action
Fast	Silence	Above best-glide. Positive energy margin.	No action.
L/D~MAX~ → ONSPEED	Low-pitch pulsing (slow → fast)	Decelerating into the approach range. Start of low-pitch tone ≈ V~Y~ / best glide.	Normal deceleration.
ONSPEED	Solid 400 Hz tone	Balanced effective power — V~X~ / V~REF~ / max sustained turn rate.	Hold this.
Below ONSPEED	High-pitch pulsing (slow → fast)	Energy deficit — unsustainable.	Push: throttle, nose down, or both.
Stall warning	High-pitch buzz (20 pps)	At the aerodynamic limit.	Unload — reduce AoA immediately.

The Push / Pull Decision

The pattern alone tells you the action — no airspeed lookup required:

High-pitch pulsing → push (throttle forward, nose down, or both)
ONSPEED solid tone → hold; you are balanced
Low-pitch pulsing → pull (throttle back, allow pitch to increase)
Stall warning buzz → unload immediately

Logic is the same in level flight, in a turn, climbing, or descending — AoA-based, so the tones automatically account for bank, weight, and load factor.

Mapping to V-Speeds

For N720AK, the OnSpeed tone progression maps approximately to the published V-speeds:

Tone	Approximate condition
Start of low-pitch tone	V~Y~ / best glide (~95 KIAS clean)
ONSPEED solid tone	V~X~ / V~REF~ approach (~80 KIAS clean)
Stall warning buzz	Approaching V~S~ for the configuration

Speeds vary with weight, bank, and configuration — fly the tone, not the airspeed.

Audio Routing

OnSpeed audio is delivered to the headsets via the Dynon PFD audio output, mixed through the GMA 245 audio panel.

Muted Mode

If the pilot mutes audio:

All tones go silent except the stall-warning buzz, which overrides mute as a safety feature.
Stall warning in mute fires only if AoA > stall threshold AND IAS > the mute-under-IAS setting (default 25 KIAS).

Pin	Function	Wire Color
1	12V power (from PFD, 2A fuse)	Red
4	Ship ground	Black

Data Inputs

Pin	Function	Wire Color
21	Flap pot wiper	White
25	EFIS serial4 TX line	Blue

Button / Lower Console

Pin	Function	Wire Color
5	Ground (to “−” on button, “C1” on button, volume pot “−/CCW”, pilot lo)	Black
2	Volume pot CW	Red/white
9	Volume pot wiper	Orange/white
11	“+” on button	Orange/blue
23	“NO1” on button	Brown/white

Control cable wiring (6-conductor, button to OnSpeed box):

Wire	Color
1	Red/white
2	Orange/white
3	(none)
4	Orange/blue
5	Brown/white
6	Black

Headset Audio Output

Pin	Function	Wire Color
10	Pilot audio right	Purple/green
22	Pilot audio left	Purple/yellow

Inspection & Maintenance

References

AMX-10A Installation Diagram 1
AMX-10A Installation Diagram 2
AMX-10A Installation Diagram 3
OnSpeed Calibration Configs (Public/Configs/OnSpeed/)
OnSpeed Documentation (web-based — installation, calibration, troubleshooting)

Pilot's Operating Handbook