GPWS

GPWS (Ground Proximity Warning System, pronounced jip-wiz) warns the crew about unsafe descent, terrain closure, clearance and approach conditions. Rise also provides predictive terrain and obstacle awareness using the terrain and city/colony geometry received by the client.

Pilot controls and indications

Control	Default binding	Current Rise behavior
GPWS Test / GS Cancel	Shift+F11	On the ground, start or cancel the functional self-test. In flight, cancel Mode 5 glideslope alerts. Other hazard modes remain available.
GPWS Hazard Inhibit	Shift+F12	Toggle hazard inhibition. GPWS INHIBIT is a steady, silent CAS status. Mode 6 advisories, including bank and altitude callouts, remain separately controlled.

Bindings can be reassigned in the GUI. Existing custom assignments may differ from these defaults.

Cockpit integration

• GS CANCEL appears on CAS and remains set until touchdown.
• The normal moving map is the default. There is no pilot terrain-view toggle and no exposed GRND PROX TERRAIN switch.
• On the E-10, E-11, T-19, P-13 and T-27, an active GPWS hazard automatically selects and keeps the MFD on Moving Map. Clearing the hazard leaves that page selected. This applies to reactive cautions/warnings as well as predictive terrain/obstacle alerts; routine bank and altitude callouts do not change pages. Hazard inhibit, self-test, ground operation and the in-world simulator do not force a page change. The A-4 and W-6 already have separate permanent map displays.
• A predictive terrain or obstacle caution/warning automatically selects the terrain overlay. Clearing the threat restores the normal map and the previous range. With default auto-range enabled, an encounter selects the 10 km inner / 20 km outer range once.
• A bank callout, altitude callout or other reactive GPWS mode does not by itself select the terrain overlay. Reactive hazard text can still appear on the map.
• On the ground, the normal map is shown and flight-hazard alerts are suppressed. Ground status alone does not mean GPWS is inoperative. Self-test and departure callouts are separate functions.

GPWS INOP indicates invalid radio-altitude or air-data inputs; it is not a normal parking indication. Position failure can make terrain awareness unavailable independently. GPWS TEST and test patterns remain on the PFD/MFD. Routine inhibit/cancel status belongs on CAS, rather than across the map.

Predictive terrain and obstacle awareness

Look ahead as well as down. Enhanced terrain awareness compares the flight path with terrain and obstacles ahead. It is separate from Mode 2, which reacts to measured terrain closure beneath the aircraft. Runway-dependent look-down limits allow a normal approach without projecting the descent endlessly through the runway.

Rise tests both the fine inner terrain mesh and the coarse distant mesh, plus solid components of received cities and colonies. It uses ground-relative movement, vertical speed and observed turns. Buildings are classified as obstacles; ground-level paving and non-solid crops are excluded. A structure in the path can therefore produce CAUTION OBSTACLE over otherwise low, green terrain.

Threat	Caution announcement	Warning announcement
Terrain	“Caution terrain. Caution terrain.”	“Terrain. Terrain.”, followed by plain “Pull up.” while the warning persists
Obstacle	“Caution obstacle. Caution obstacle.”	“Obstacle. Obstacle.”, followed by plain “Pull up.” while the warning persists

Warnings outrank cautions. At equal predictive severity, terrain takes priority over obstacle, so minor changes in encounter timing do not continually exchange the two announcements. A standalone “Terrain.” is also used by reactive Mode 2; there is no standalone predictive “Obstacle.” callout.

Prediction envelope and data

• Nominal look-ahead: 60 seconds for caution and 30 seconds for warning. At 300 knots ground speed or more, the warning horizon can extend toward 60 seconds using an 8 NM extension-distance limit; it never becomes shorter than 30 seconds. The total scan has a 60 km range cap.
• Nominal vertical margin: 500 ft / 152.4 m. This narrows during low-altitude takeoff/landing and an accepted runway approach. It is a clearance margin, not an alert at every height below 500 ft.
• The corridor starts 0.25 NM wide, expands 3° on each side and includes vehicle radius. Observed turns are extrapolated for ten seconds, then along the resulting tangent.
• Only received geometry is known. There is no certified worldwide terrain/obstacle database or airport-specific modulation catalog. Unknown data is not assumed to be flat or safe.
• These advisory margins do not guarantee clearance during an escape maneuver.

GPWS uses the latest available sensor and terrain information. Low or uneven frame rates can increase response latency; missing or stale data must not be treated as complete sensor coverage.

Alert stability

Immediate alerts, confirmed clearance. New predictive cautions and warning escalation appear on the next eligible GPWS scan. A currently received terrain cell or building retains its warning until it has gone two seconds without warning detection, and retains its caution until it has gone two seconds without either caution or warning detection. Brief prediction changes therefore do not repeatedly switch the terrain popup, highlighted hazard, message and automatic range. The clearance delay stabilizes the annunciation; terrain heights and flight-path inputs are not averaged or delayed.

The same retained state feeds the map and spoken-alert selection. Warning still outranks caution, and terrain precedes obstacle at equal severity. After confirmed clearance, the normal map and previous range return; obsolete queued predictive speech is discarded and an ordinary playing phrase finishes. The existing two-second warning and seven-second caution repeat cadences remain separate from this release timer. A solid yellow patch may be a terrain cell: read CAUTION TERRAIN versus CAUTION OBSTACLE to identify the selected hazard category.

History follows terrain cell identity and building bounds, so grid shifts or building-list reordering cannot transfer a retained highlight to a different object. Missing/invalid geometry or an unloaded building loses its history immediately; data-limited indications remain current. Ground/taxi, ground vehicles, hover below the existing forward-prediction speed limit, power loss, inhibit, self-test, simulator entry, invalid inputs, vehicle changes and high-altitude prediction suspension clear retained threats. Manual/Autoflyte changes do not reset a valid encounter. Normal atmospheric flight and fast re-entry retain immediate detection; suborbital/orbital suspension keeps the separate geometric rules below. Reactive protection remains separate, including near-ground VTOL/hover protection. Re-arming requires a current detection.

Runway approaches and VTOL

Runway recognition. An aligned, converging approach to a selected or inferred received runway can be recognized within the existing 42.6 km guidance range. It works for hand-flown approaches and before gear extension. The runway must have valid position, heading and length; track, height and descent must remain compatible with the approach. Selecting a waypoint or capturing LOC/G/S alone does not suppress alerts.

The expected descent is bounded by the runway profile and ends at the runway end. Terrain and structures that penetrate that protected path still alert. A wrong course, excessive descent or loss of the approach geometry removes the allowance; landing configuration alone is not permission to fly into a hazard. Independent terrain/runway clearance floors remain active.

VTOL and off-runway landing. Vertical-thrust capability plus an appropriate selected touchdown point permits a limited close pad-approach allowance: gear down, destination ahead within 5 km, less than 600 m above it, and within the lateral/descent/turn checks. This is not an automatic helicopter landing funnel around every selected waypoint. At hover there is no invented forward travel, but descent and clearance protection still matter.

Terrain display colors

Relative height coloring and a predicted conflict are different things. Green ground is not a caution. The warning/caution label and solid hazard highlight identify an actual predicted conflict.

Appearance	Meaning
Green / dark relative shading	Terrain below aircraft altitude. Lower bands are darker; Peaks uses green elevation bands when no yellow/red relative terrain is in view.
Yellow relative shading	Terrain near or above aircraft altitude. The near-height band starts 500 ft below the aircraft, or 250 ft below with gear down. Higher yellow bands use denser stippling.
Red relative shading	Terrain more than 2,000 ft above the display's reference altitude.
Solid bright yellow hazard	Predicted caution: the affected terrain or obstacle is highlighted, with CAUTION TERRAIN or CAUTION OBSTACLE.
Solid red hazard	Predicted warning, with TERRAIN - PULL UP or OBSTACLE - PULL UP.
Magenta	Missing terrain data within the represented map coverage. It does not mean terrain is above the aircraft.
Cyan / black	Known water / low or decluttered terrain. Black alone is not a guarantee of clearance.

Descent faster than 1,000 ft/min biases the displayed reference downward by thirty seconds of descent. Sparse/dense stippling distinguishes relative bands from solid threats. Known terrain within 400 ft of a nearby received runway elevation is decluttered unless it contains a detected threat. These colors describe the terrain overlay when active; they do not replace the normal map while parked.

Display patterns: sparse/dense patterns use 25%/50% coverage. The Peaks green range is divided into thirds, and known Vieneo water is identified from world data rather than assuming Earth sea level.

TERR DATA LIMITED and OBST DATA LIMITED identify incomplete prediction coverage. Known hazards can still alert. TERR DATA LIMITED has no black backing; active hazard labels retain their backing for readability. A fully absent mesh cannot be painted as if it were known terrain.

Predictive high-altitude suspension

Terrain scanning in ascent and re-entry. The predictor considers the lowest altitude projected over the next 60 seconds, including descent. Its reference ceiling is 11.44 km MSL: Vieneo's 9.525 km highest terrain + 915 m maximum structure + a 1 km margin. An active scan suspends above 11.69 km projected minimum altitude; a suspended scan resumes at or below 11.44 km. This 250 m separation prevents repeated switching. Rapid descent can therefore require prediction while the aircraft is still much higher. Data-limited annunciations are suppressed while prediction is intentionally suspended.

This is separate from the bank-advisory rules below. There is no single altitude switch that disables all GPWS, TCAS or weather-radar functions.

Reactive GPWS modes

The modes below use current aircraft state and measured clearance/closure. They remain distinct from predictive terrain/obstacle awareness. Their spoken alerts pass through the same voice management system.

The graphs show each mode in isolation; power, airborne state, valid inputs, configuration, inhibits and alert priority still apply. Plot shading is an illustration aid, separate from the cockpit terrain-color legend. Click a graph for the full-resolution image. Height axes use feet (1 ft = 0.3048 m).

Mode 1 — Excessive descent rate

Mode 1 default Rise envelope. Purple marks the numerical Rise approximation; this plot excludes steep-approach and above-glideslope capture biases.

“Sink rate” warns of excessive descent; deeper penetration produces “Whoop whoop, pull up.” It does not require a particular gear/flap configuration.

Operating conditions: active from 50 to 2,450 ft AGL. Steep-approach selection adds the 500 ft/min caution and 200 ft/min warning biases. It resets on landing/go-around.

Mode 2 — Excessive terrain closure

Mode 2A/2B reactive closure envelopes. Purple: current Rise curves. Blue dashed line: the cap with terrain awareness available. The fully configured Mode 2B case suppresses Pull Up.

rapid closure produces “Terrain, terrain” and, when appropriate, “Whoop whoop, pull up.” Mode 2B reduces nuisance alerts in landing/airport conditions. Fully configured landing uses the single “Terrain” warning instead of Pull Up.

Operating conditions: Mode 2B is selected by landing flaps/override, centered valid ILS, the first 60 seconds after takeoff, or the selected runway vicinity with terrain awareness available (10 NM / 3,500 ft). Mode 2A's speed-dependent upper cap is 1,500–2,000 ft, reduced to 950 ft with available terrain awareness; Mode 2B uses 200–790 ft. After a Mode 2A Pull Up, single Terrain can continue while closure persists. The visual latch clears after 300 ft climb, 45 seconds, or landing flaps/override.

Mode 3 — Altitude loss after takeoff or low go-around

Mode 3 altitude-loss threshold. The shaded region produces a Don’t Sink alert when the mode is armed.

“Don't sink” responds to loss of geometric altitude, rather than mistaking rising terrain beneath a climbing vehicle for a descent. It arms after takeoff or a low go-around, applies when not fully configured for landing, and recovers with positive climb.

Alert threshold: the altitude-loss threshold is 8 − 3h meters, where h is radio altitude in kilometers; the takeoff phase ends above 1,500 ft AGL.

Mode 4 — Unsafe terrain clearance

Modes 4A, 4B and 4C are implemented.

Mode	Condition and behavior
4A — gear up	In cruise/approach, “Too low gear” below 500 ft at up to 190 knots IAS; at higher speed, “Too low terrain” uses the expanding clearance floor, up to 1,000 ft at 250 knots.
4B — gear down, flaps not in landing position	“Too low flaps” below 245 ft at up to 159 knots IAS; at higher speed, “Too low terrain” uses the expanding floor, up to 1,000 ft at 250 knots. Flap override treats the flap condition as satisfied.
4C — takeoff/low go-around	“Too low terrain” if clearance falls to the nondecreasing floor based on 75% of the preceding 15 seconds' radio height, when not fully configured for landing.

Available terrain awareness removes the Mode 4 speed expansion: 4A/4C retain a 500 ft cap and 4B a 245 ft cap. A/B operate from 50 ft AGL and include level flight; descent is not required.

Mode 4A: gear-up clearance floor. Blue shows the speed-dependent clearance floor; the dashed line shows the available-terrain-awareness cap.

Mode 4B: gear-down, flaps-not-landing clearance floor, including the available-terrain-awareness cap.

Mode 4C: blue clearance-history floor with a purple illustrative flight path. This example shows why the floor does not fall when the aircraft begins descending; it is not measured flight data.

Mode 5 — Below glideslope

Mode 5 for a qualifying approach descending at least 500 ft/min. Blue: nominal dot thresholds. Purple: the current Rise regions and near-ground approximation. The upper height limit reduces toward 500 ft in level flight.

A valid front-course ILS can qualify a hand-flown approach; Autoflyte G/S capture is not required. The upper radio-height limit varies from 500 to 1,000 ft with descent rate. The soft region begins at about 1.3 dots low; the hard region is below 300 ft and at least about two dots low. Both become less sensitive very near the ground, and no Mode 5 alert occurs below 50 ft.

Soft Glideslope uses half-volume and repeats with further deviation. Hard Glideslope plays two complete phrases at normal volume on a four-second cycle. Higher-priority hazards take precedence. Use GPWS Test / GS Cancel in flight to cancel this mode until touchdown.

Mode 6 — Advisory callouts

Altitude and minimums

Implemented descending radio-height callouts are 1,000, 500, 200, 100, 50, 40, 30, 20 and 10 feet. Installation settings can disable individual heights. The 500-foot call can be unconditional, smart, above-field, or externally controlled/disabled. “Minimums, minimums” uses the configured radio decision height (default 200 ft) and requires gear down.

Each height is consumed once per approach. If descent crosses several heights while speech is busy, obsolete pending heights are discarded and the latest relevant callout is retained. Mode 6 advisories do not illuminate GPWS hazard lamps.

Operating note: above-field uses geometric height over a received runway. There is no separate barometric MDA/Approaching Minimums installation. Rotate, Positive Rate and Retard are additional crew callouts.

Bank angle — manual and Autoflyte

The actual Autoflyte engagement state selects the profile; flight-director guidance alone does not count as engagement. Bank magnitude is the same for left and right turns, and must exceed the threshold. After the first call, a further 20% increase in bank permits another announcement. After three escalating announcements, persistent bank at or above that last level can repeat every two seconds. Recovery clears the encounter.

Blue/teal: the manual and Autoflyte bank profiles. Purple: Rise's additional spaceflight policy. The graph's height axis is logarithmic; the thresholds increase linearly with height within each ramp.

Radio height AGL	Manual	Autoflyte
Below 5 ft / 1.524 m	Inhibited	Inhibited
5–30 ft / 1.524–9.144 m	10°	10°
30–122 ft / 9.144–37.186 m	10→33°	10→33°
122–150 ft / 37.186–45.720 m	33→40°	33°
150–2,450 ft / 45.720–746.760 m	40→55°	33°
Above 2,450 ft in normal atmospheric flight	55°	33°
Rise spaceflight/hypersonic exclusion, above 762 m AGL	Inhibited	Inhibited

Normal atmospheric flight above 2,450 ft AGL retains the 55° manual or 33° Autoflyte bank threshold, subject to the spaceflight rules below.

Rise spaceflight and re-entry rules

Bank advisories only

• At or below 762 m AGL (2,500 ft): near-ground protection overrides the spaceflight exclusion. The ordinary bank profile and 5 ft minimum still apply. Low IAS, a stall or a hover does not disable it.
• Above 762 m AGL: enter the exclusion when modeled mass density is at most 1% of surface density OR Mach is at least 5.
• Re-arm: density must recover to at least 2% AND Mach fall to 4 or below, or the aircraft must return to the near-ground band. The different entry/recovery thresholds prevent chatter.
• With the client's 7.5 km density scale height, the density crossings are approximately 34.54 km MSL and 29.34 km MSL. These are MSL equivalents, not AGL thresholds. The model is exp(−|MSL|/7.5 km), sampled at the current position.
• Obsolete queued bank calls are removed; an ordinary phrase already playing finishes. Ground, power and vehicle resets clear the exclusion history.
• This policy also covers hypersonic atmospheric flight. It is not an orbital-state detector or a calculation of remaining aerodynamic control authority. It does not disable terrain interception, obstacle awareness, TCAS or weather radar.

The bank-advisory rules use Vieneo's atmospheric mass density, rather than pressure or IAS alone. IAS can also be low during a near-ground stall, backwards flight or hover, so low IAS by itself does not silence the advisory.

Additional clearance and windshear functions

Terrain Clearance Floor / Runway Field Clearance Floor: separate “Too low terrain” protection compares radio clearance and geometric height above received runway elevation with distance-dependent floors. It remains independent of landing configuration and the predictive runway allowance. Position-integrity settings affect the inner bias. Only received runway data is available; the client does not synthesize a worldwide airport database.

Mode 7 — Reactive windshear

Reactive windshear detection responds to changes in wind encountered by the aircraft. Predictive windshear is a separate forward-looking weather-radar function; the presence of Mode 7 alone does not imply forward-looking detection.

Wind inputs. The detector uses signed headwind change and local-vertical wind, including gusts. A headwind becoming a tailwind is treated as a loss of headwind even when the two wind speeds have equal magnitudes.

Wind change is measured over a rolling one-second interval using sensor timestamps, independently of rendering frame rate and the map wind readout. Turning in steady wind does not create artificial shear. Unchanged samples retain their result; input older than two seconds is discarded. Reset or recovered input starts a fresh history: horizontal change needs one second, while vertical-wind protection is immediate.

Operating band: 10–1,500 ft AGL, powered and airborne, with valid inputs and hazard inhibit off. Rise protects APN and ACL flight, including level flight and VTOL/hover. Low IAS does not disable it, and it never divides by airspeed. With no ground track, it uses the aircraft's horizontal nose direction; if that also cannot be defined, vertical-wind protection remains available. Ground, vehicle/simulator transitions, invalid inputs and leaving the band clear the history. Re-entry into the band re-arms it. The separate bank-advisory spaceflight exclusion does not suppress fast near-ground windshear protection.

Alert threshold: let H be the one-second headwind change in knots/second (positive for increasing headwind), and W the local updraft in feet/minute. The detector uses S = W + 750 H: below −1,750 warns; above +1,750 cautions. These advisory thresholds do not calculate the aircraft’s remaining escape performance.

Windshear alerts use complete phrases and discard stale queued warnings. Persistent windshear has a four-second repeat interval; playback waits for the current phrase to finish.

Mode 7: signed headwind change over one second versus local-vertical wind. Purple shows the caution and warning regions.

Audio behavior and self-test

These GPWS alerts use the command bus and VMU queue. Predictive cautions contain the doubled phrase in one recording and repeat on a seven-second cadence. Persistent predictive warnings use plain Pull Up on a two-second repeat cadence after the initial Terrain Terrain or Obstacle Obstacle phrase. Reactive Pull Up retains its whoop-whoop recording. Actual playback waits for the current phrase to finish; these timers do not restart a clip mid-word.

The automatic overspeed clacker is a separate continuous warning. It requires avionics power and a valid positive Vne. It stops on the next audio update when indicated airspeed no longer exceeds that limit, either speed input is invalid, or cockpit power reaches the VMU power-off cutoff (including shutdown). Invalid power data also stops it. After power returns, only a currently valid overspeed condition can re-arm it; audio reloads cannot revive it while unpowered. The E-10 has no configured Vne; an unset limit must not trigger clacking at low speed.

Finish the active phrase. Normal changes in hazard priority discard stale queued speech but let the current recording finish. Power/vehicle/simulator transitions clear invalid state rather than replaying stale warnings. Missing voice assets can leave a visual caution without its expected spoken phrase; a displayed caution is not evidence that its recording is installed.

The combined test control runs Level 1 while powered, on the ground and not inhibited. It exercises indications, complete Glideslope / Pull Up / Terrain Terrain phrases and a terrain test pattern, then ends. Takeoff, power loss, vehicle change or hazard inhibit cancels the test. Diagnostic bus commands also provide levels 2–6 for current faults, installation/data information, session fault history, session warning history and changing discretes. These histories are session-only; spoken maintenance descriptions and nonvolatile maintenance logs are not implemented.

The in-world simulator retains its baseline moving map and reactive GPWS behavior; predictive terrain/obstacle awareness is excluded there.