What the Tones Mean¶

This is the complete reference for all OnSpeed audio cues. Print this page and keep it in the cockpit until you've internalized the tone progression.

Heritage: directive vs. descriptive

Aural AOA cues for carrier landings predate OnSpeed by decades. Vac credits the Royal Navy in Go down, speed up, stall out… (post #25): "the Royal Navy hit it out of the park when they developed an aural AOA cue back in the Stone Age." The F-4 Phantom (1960s) is the most widely cited military example, and the OnSpeed tone family descends from that broader carrier-aviation lineage.

It survives because it works: it gives the pilot directive information — what to do — rather than descriptive information — what's happening — which the pilot then has to interpret and react to.

A conventional airspeed indicator is descriptive. The pilot sees a number, computes a margin to V_REF at the current weight and load factor, and reacts. Vac's framing in Angle of Attack and Energy Maneuverability (post #37):

"Conventional flight instruments present descriptive information to the pilot. That information must be interpreted, usually visually, and processed. Then the pilot must react. Assuming the pilot sees the cue, it takes about a half second to interpret and another half second to react… An AOA tone provides directive and descriptive information. Assuming the pilot hears the cue, they can respond in half of the time."

The tones below are commands as much as status reports — pull, hold, push, unload, or, in the silent fast region, no action needed. The aerodynamic state behind each (fast, ONSPEED, slow, stall warning) is the descriptive information; the action the pilot takes in response is the directive part. Both arrive in the same cue.

The lineage isn't accidental. The same tone family worked for carrier-deck pilots flying narrow approach AOA bands at night in heavy aircraft, and it works for a single-engine GA airplane on a stabilized final. The constraints on aerodynamic margin, pilot workload, and reaction time are similar enough that the directive logic transfers cleanly.

Tone Regions¶

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)
  <50% lift   ~50% lift      ~60% lift    65-90% lift    >90% lift

The percentages above are typical values; the exact percent at which each band falls is set by your aircraft's calibration and varies per flap setting. Fly the audio cues — the tones tell you where you are, and the percent number on the indexer is descriptive (after-the-fact information), not directive.

Complete Reference¶

#	Region	Tone	Pulse Rate	Fractional Lift	What It Means	Pilot Action
1	Fast	None	—	Below ~50%	Above best-glide speed. Positive energy margin.	No action needed.
2	Approaching	Low-pitch pulsing (400 Hz)	1.5 → 8.2 pps	~50–60%	Between L/D_MAX and ONSPEED. Decelerating into the approach range.	Normal deceleration.
3	ONSPEED	ONSPEED solid tone (400 Hz)	Solid (0 pps)	~60%	Balanced effective power. Thrust and drag matched for current weight.	Hold this.
4	Slow	High-pitch pulsing (1600 Hz)	1.5 → 6.2 pps	~65–90%	Effective power is negative. Unsustainable condition.	Push: add power, reduce AOA, or both.
5	Stall Warning	Stall warning buzz (1600 Hz)	20 pps	>90%	At the aerodynamic limit. Stall imminent.	Unload: reduce AOA immediately.

The Push/Pull Decision¶

The tone pattern tells you whether to push or pull:

Hear high-pitch pulsing? → Push something: throttle forward, nose down, or both
Hear the ONSPEED solid tone? → Hold: you're balanced
Hear low-pitch pulsing? → Pull something: throttle back, allow pitch to increase
Hear the stall warning buzz? → Unload for control: reduce AOA immediately

This logic works in any flight condition — straight and level, in a turn, climbing, descending.

Pulse Rate Details¶

Within the pulsing regions, the pulse rate changes linearly:

Region 2 — Low-pitch pulsing (L/D_MAX → ONSPEED): Starts at 1.5 pulses/sec at L/D_MAX (low-pitch slow tone), increases to 8.2 pulses/sec approaching the ONSPEED band (low-pitch fast tone)
Region 4 — High-pitch pulsing (below ONSPEED → Stall Warning): Starts at 1.5 pulses/sec just below ONSPEED (high-pitch slow tone), increases to 6.2 pulses/sec near the stall warning threshold (high-pitch fast tone)

The stall warning buzz (Region 5) is a fixed 20 pulses/sec — an unmistakably urgent buzz. Volume also increases in the slow region, and the stall warning buzz overrides any audio muting.

Key Performance Conditions¶

Each tone region corresponds to well-defined aerodynamic performance conditions:

Stall Warning (>90% Lift)¶

Aerodynamic limit — maximum instantaneous turn capability just prior to stall
No sustainable maneuvering margin
The wing cannot produce more lift

ONSPEED (~60% Lift)¶

Balanced effective power at any flight condition (thrust and drag balanced as a function of velocity)
Maximum sustained turn rate
V_REF (approach reference speed)
Best angle of climb (V_X)
Maximum endurance
Optimum low-altitude maneuvering
Best blend of turn and glide performance, with appropriate energy for landing transition and safe stall margin

The ONSPEED band is approximately ±1° of AOA, resulting in an airspeed band of approximately ±2–3 knots at 1G.

"Slightly Fast" (~50–55% Lift)¶

Increased stall margin for gusty or turbulent conditions
Fly here when conditions warrant extra margin

L/D_MAX (~50% Lift)¶

Maximum range (no-wind)
Maximum range glide (best glide)
Approximate best rate of climb (V_Y)

Maneuvering Speed (varies with aircraft G-limit)¶

The fractional lift associated with V_A
Determined by dividing 100% by the airplane's positive G-limit
For a normal-category airplane (3.8G limit): ~26% lift
Below this value, the airplane will stall before reaching the structural limit

Tone Transitions in Practice¶

Here's what you hear during a typical approach in an RV-4 (flaps 0°, ~2300 lbs):

Speed (KIAS)	Tone	What's Happening
120+	Silence	Downwind — wing at low lift fraction
100	Silence	Base turn — still above L/D_MAX
~87	Low-pitch slow tone	At L/D_MAX — best glide speed
80–75	Low-pitch pulsing, speeding up	Decelerating through the approach range
~72	ONSPEED solid tone	ONSPEED — balanced effective power
68	High-pitch slow tone	Below ONSPEED — energy deficit
65	High-pitch fast tone	Getting slow — correct now
~62	Stall warning buzz	Stall warning — unload immediately

Your speeds will be different

These speeds are examples for a specific aircraft and weight. After calibration, the tones match your aircraft's characteristics. The beauty of AOA-based tones is that the same AOA thresholds apply regardless of your current weight or G-loading — the tones automatically account for bank angle, weight, and any other factor that changes stall speed.

How Angle of Attack Relates to Speed¶

As airspeed decreases, angle of attack increases — but not linearly. AOA increases more rapidly as you slow down. Approximately half of the wing's lift-producing capability is used in the lower third of the airplane's speed range. This is why maneuvering near approach speeds can quickly become hazardous: angle of attack rises rapidly with even small increases in G.

The tone regions are spaced to reflect this reality. The "slow" region (high-pitch pulsing) covers a smaller speed range but a rapidly changing AOA range, giving the pilot progressively more urgent cueing as margin decreases.

Muted Mode¶

If you press the audio mute button:

All tones go silent
The stall warning buzz still sounds (safety override)
To unmute, press the button again

The stall warning in muted mode only fires if both conditions are met:

AOA is above the stall warning threshold
IAS is above the mute-under-IAS setting (default: 25 knots)

Gen3 feature

The stall warning override in muted mode is a Gen3 feature. Gen2 units do not override the mute for stall warnings.