altimeter
Enable an AI agent to identify an altimeter, interpret its altitude indications, assess whether those indications are usable and determine which adjustments, checks or restrictions are appropriate.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to identify an altimeter, interpret its altitude indications, assess whether those indications are usable and determine which adjustments, checks or restrictions are appropriate.
An altimeter is an instrument that reports the vertical distance of a platform from a declared datum (mean sea level, a standardised isobaric surface, or the underlying terrain) by converting a physical observable - static pressure, radio or optical round-trip delay, or GNSS-derived height - into indicated, encoded, or control altitude.
It can be Read or retrieve an altitude indication together with its units, reference, timestamp and validity.; Inspect or adjust a supported pressure reference or local-zero setting under the applicable procedure.; Compare indications against a suitable reference or independent altimeter after reconciling datums and settings.; Inspect input availability and run supported diagnostic or functional checks.; Identify readings that require restriction because of faults, stale data or operation outside documented limits.; Arrange calibration, repair or inspection and record the evidence required before further use..
Distinguishing features
Its intended output is altitude or height relative to an identifiable reference, rather than pressure alone; a pressure gauge needs a documented altitude-conversion function to qualify.
It provides a current altitude or height indication or output; a vertical-speed-only instrument reports rate of change and does not independently satisfy this test.
Its measured or derived quantity represents vertical position or clearance; an arbitrary target-distance reading does not establish that a rangefinder is an altimeter.
For a multifunction device, the altitude function, its reference and its validity can be identified separately from navigation, position or environmental functions.
Scope
+ Altimeter identity, measurement principle and intended use
+ Altitude reference, units, settings and interpretation of indications
+ Pressure, signal, power and mounting dependencies that affect altitude output
+ Accuracy evidence, operating limits, faults and indication validity
+ Controls, calibration, inspection and return-to-service evidence
- The aircraft, vehicle, wearable or other platform carrying the altimeter
- Weather systems and atmospheric forecasts
- Terrain databases, maps and surveyed reference networks
- Navigation receivers, air-data computers and sensor networks except at the altimeter interface
- Flight procedures, route planning and platform-wide safety decisions
- General-purpose pressure gauges and rangefinders without an altitude-measurement function
Characteristics
- Measurement principle
- Pressure-based, radio/radar, satellite-derived, other documented principle or hybrid Determines which inputs, assumptions and failure modes must be checked before interpreting altitude.
- Implementation boundary
- Standalone instrument, sensor module, display of externally computed altitude or integrated function Locates responsibility for sensing, computation and presentation.
- Altitude reference
- Named pressure reference, named vertical datum, reflecting surface, local zero or unknown Two readings cannot be meaningfully compared without establishing their references.
- Indicated altitude or height
- Metres or feet, with observation time, reference and validity Records what the instrument currently reports without treating the indication as independently verified truth.
- Reference setting
- Pressure in hPa or inHg; altitude offset in metres or feet; not applicable where unsupported A changed setting can change the indication without physical movement.
- Supported measurement envelope
- Documented minimum and maximum altitude or height, with applicable conditions Separates a displayed value from a value within the instrument's supported range.
- Accuracy and resolution evidence
- Links to specifications and test results identifying units, conditions, uncertainty and display increment Prevents display precision from being mistaken for measurement accuracy.
- Output freshness
- Sample age and latency in seconds; update rate in Hz where applicable An apparently plausible indication may be stale during changing altitude.
- Input dependencies
- Associated pressure sources, antennas, receivers, processors, power supplies and data links Makes upstream faults and shared dependencies visible.
- Indication validity
- Valid within documented conditions, degraded, invalid, unavailable or unknown Supports restrictions on use without equating a working display with a trustworthy measurement.
- Service condition
- Unchecked, serviceable with evidence, restricted, due for inspection or out of service Connects permitted use to inspection and maintenance evidence.
Also called
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.altimeter
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 30 questions.
Altitude function and reference Establishes what the instrument measures and what its altitude means.
Altitude indications from different principles or references can look interchangeable while representing different quantities.
Measurement function
Identifies the altimeter function and the boundary between sensing, computation and display.
Altitude-producing chain
Record the documented principle and the components that turn an input into altitude.
- Does this altimeter derive altitude from pressure, returned signals, satellite positioning or another documented input? definition
- Which identified component senses the input, computes altitude and presents or transmits the result? boundary
Vertical reference
Makes the datum or reference setting explicit.
Meaning of zero
Record the reference that gives zero and other indicated values their meaning.
- What pressure reference, vertical datum, reflecting surface or local zero does the current output use? definition
- What source established the reference or setting, and when was it last confirmed? provenance
- Which apparent altitude comparisons are invalid until reference differences are resolved? boundary
Indication and interpretation Captures the altitude output and the information needed to read it correctly.
A number or pointer position is insufficient without units, scale, timing and validity.
Readout semantics
Describes the particular display or output encoding.
Unambiguous altitude reading
Record how the complete altitude is recovered from pointers, digits or transmitted fields.
- How are units, sign, scale and any multiple pointers or digit windows combined into one altitude reading? measurement
- How does this instrument distinguish an out-of-range, unavailable or invalid output from a usable altitude? definition
Output timing
Connects a reading to when it was sensed and reported.
Freshness and response
Record available evidence about update timing, lag, filtering and retained values.
- What observation time, sample age or documented response lag applies to this reading? measurement
- Can the output freeze, retain a last-known value or smooth changes, and how can an agent detect that condition? boundary
Sensing and installation dependencies Connects altitude production to the instrument's actual inputs and installation.
Altitude errors may originate in pressure delivery, signal reception or installation even when the instrument appears operational.
Input path
Identifies the inputs required by this particular measurement principle.
Required input condition
Record input sources, their condition and evidence of successful delivery.
- Which pressure connection, antenna, receiver or external altitude-data source supplies this altimeter? boundary
- What observable checks establish that each required input is available and suitable for altitude measurement? measurement
Installation effects
Captures mounting and shared-system conditions that can affect the output.
Installation-specific altitude errors
Record documented installation constraints and dependencies relevant to altitude validity.
- Which documented constraints on pressure-port location, antenna orientation, mounting or local interference apply to this installation? boundary
- Does an apparent comparison instrument share the same pressure source, receiver, processor or power supply? provenance
Measurement confidence and limits Determines where altitude indications are supported and how their reliability is assessed.
An agent needs evidence that a reading is fit for its intended use, beyond the presence of an output.
Supported envelope
Records principle-specific and device-specific operating limits.
Applicable altitude performance
Associate range and performance claims with their documented conditions.
- What altitude or height range and environmental or signal conditions are covered by the available specification? boundary
- What accuracy, resolution and response requirements apply within that envelope, and what evidence supports them? provenance
Validity assessment
Interprets fault indications and comparison results.
Altitude disagreement and faults
Record discrepancies without assuming either instrument or reference is correct.
- After reconciling reference, units and observation time, how far does the indication differ from the chosen comparison? measurement
- Which observed flags, input failures or discrepancies require the reading to be restricted or rejected under the applicable procedure? action
- What remains uncertain about whether a discrepancy comes from the altimeter, its inputs or the comparison reference? boundary
Settings, checks and service Defines supported interventions and the evidence needed to continue using the altimeter.
Reference adjustment, calibration and repair change different aspects of altitude interpretation and require distinct controls.
Operational adjustments
Records the settings an operator or agent may change.
Controlled reference change
Track supported setting changes and their effect on altitude meaning.
- Which pressure-reference, zero, unit or correction settings are available, and who may change them? action
- What source and procedure justify a setting change, and what resulting indication should be checked? action
Verification and restoration
Connects checks and maintenance to evidence of usable altitude performance.
Documented altimeter serviceability
Record inspections, calibration results, unresolved defects and conditions for renewed use.
- Which inspection or calibration procedure applies to this altimeter and installation, and what does the latest result establish? provenance
- After a failed check, repair or relevant installation change, what verification and authorization are required before further use? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Pressure (barometric/aneroid) altimeter, including the sensitive cockpit instrument with a Kollsman subscale
- Radio/radar altimeter, measuring height above ground by 4.2-4.4 GHz ranging
- Encoding altimeter or separate altitude encoder for Mode C/S transponder reporting
- GNSS/satellite altimeter (ellipsoidal or geoid-referenced height)
- Laser/LiDAR altimeter (airborne and satellite topographic and ice-sheet ranging)
- Cabin-pressure altimeter used in pressurisation and oxygen systems
- Wrist, handheld, and hiking barometric altimeters
- Servoed or air-data-computer altimeters that drive electromechanical or glass-cockpit displays
- Which of these kinds and varieties hold for the sense of altimeter this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q182628 - Item for the instrument class "altimeter"; radio/radar altimeter is a distinct item.
- ITU / ICAO radio-altimeter band - 4200-4400 MHz - Allocated airborne radio-altimeter frequency band, not a product code.
- FAA TSO - TSO-C10 (pressure); TSO-C67 (airborne radar altimeter) - Equipment-approval marks on civil units, not a universal taxonomy of the thing.
- Which of these identifiers and schemes hold for the sense of altimeter this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- ICAO Annex 6 (Operation of Aircraft) and Annex 2/Doc 4444 altimeter-setting (QNH/QNE) and transition altitude/level procedures - International Civil Aviation Organization
- ICAO Annex 10 and associated SARPs/guidance on airborne radio altimeters - International Civil Aviation Organization
- FAA TSO-C10 (pressure altimeter systems) and TSO-C67 (airborne radar altimeter equipment); 14 CFR airworthiness and operating rules on altimeters and static systems - Federal Aviation Administration
- RTCA DO-155 and later radio-altimeter MOPS used as the industry performance baseline - RTCA
- EASA CS-23/CS-25 and associated ETSO material for altimeters and radio altimeters - European Union Aviation Safety Agency
- ISO 2533 International Standard Atmosphere as the pressure-altitude conversion model used by pressure altimeters - International Organization for Standardization
- National 5G C-band deployment rules and aviation mitigations addressing radio-altimeter interference (e.g. FAA/FCC actions in the United States) - national spectrum and aviation authorities
- Which of these standards and regulation hold for the sense of altimeter this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Primary cockpit altitude reference for en-route flight, approach minima, and terrain clearance; radio altimeter supplies height AGL and decision-height cues, especially for CAT II/III approaches and TAWS/GPWS.
- Mode C/S transponders and ADS-B report pressure altitude from an encoding altimeter or air-data computer.
- METAR/ASOS "altimeter setting" (QNH) is the value crews wind into the Kollsman window so indicated altitude matches elevation at the airport.
- Mountaineering, parachuting, hang-gliding, and sports watches use barometric altimeters for height and accumulated climb.
- Satellite laser altimeters (e.g. ICESat-class, CryoSat-class missions) map ice-sheet, sea-surface, and land elevation.
- Cabin altimeters and pressurisation controllers display equivalent cabin altitude and drive oxygen-mask deployment.
- Small UAS and some automotive/industrial systems use ultrasonic, radar, or barometric altimeters for height-hold and landing.
- Which of these real-world use hold for the sense of altimeter this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Indicated / pressure altitude (civil aircraft sensitive altimeter) - -1000 to 50000 (some types to ~80000) - ft
- Altimeter subscale setting (Kollsman window) - 28.00-31.00 inHg, or about 950-1050 - inHg or hPa
- Radio altitude (civil low-range) - 0-2500 (some military/high-range units higher) - ft AGL
- Hiking/wrist barometric altitude - about -500 to 9000 - m
- Radio-altimeter carrier frequency - 4200-4400 - MHz
- Pressure-altimeter tolerance near sea level (sensitive types, order of magnitude) - on the order of ±20 at sea level, growing with altitude - ft
- Which of these typical measurements hold for the sense of altimeter this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Incorrect QNH/QFE/QNE setting, causing the aircraft to fly lower (or higher) than intended and contributing to controlled flight into terrain.
- Blocked, iced, or mis-plumbed static ports, giving frozen or grossly wrong indicated altitude.
- Cold-temperature error: true altitude is lower than indicated when the column is colder than ISA, critical on non-precision approaches.
- Three-pointer analog misreading (thousands vs hundreds of feet), a classic accident factor.
- Radio-altimeter interference from adjacent-band 5G C-band transmitters, degrading height-AGL and autoland/TAWS inputs.
- Transponder/encoder mismatch so ATC sees a different altitude than the crew.
- GNSS vertical error or geoid-model mismatch when GNSS height is treated as barometric altitude.
- Servo, air-data-computer, or electrical failure of remote-indicating altimeters without a usable standby.
- Which of these failure modes and hazards hold for the sense of altimeter this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- United States and Canada set and report altimeter setting in inches of mercury; most of the rest of the world uses hectopascals (millibars).
- QNH is the civil default; QFE remains in some military, older UK, and post-Soviet practice; flight levels use QNE (1013.25 hPa / 29.92 inHg).
- Transition altitude is a national value (18,000 ft in the U.S. NAS; often 3,000-6,000 ft or a published TA in Europe and elsewhere).
- China, Mongolia, North Korea and some other states assign metric flight levels; most ICAO states use feet.
- U.S. usage often says "radar altimeter"; ICAO/EASA documents prefer "radio altimeter" for the same AGL ranging instrument.
- Which of these regional variation hold for the sense of altimeter this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Vertical-speed indicator (variometer) - Reports rate of change of altitude, not altitude itself; a blocked static system can freeze the altimeter while the VSI still shows a transient then zero.
- Barometer - Stops at pressure; an altimeter applies an atmosphere model and a subscale datum to express that pressure as height.
- Attitude indicator - Displays pitch and bank, not height; the similar English names are the usual source of confusion.
- GNSS receiver height - Geometric (ellipsoidal or orthometric) height, independent of the pressure column; it does not replace QNH-based indicated altitude for IFR separation unless a specific procedure allows it.
- Altitude encoder / transponder - The encoder reports pressure altitude to ATC; it may be a separate box from the cockpit altimeter and can disagree with it.
- Depth sounder / fathometer - Ranges downward through water to the seabed; an altimeter ranges in air or vacuum to a pressure surface, ellipsoid, or ground.
- Hypsometer - Infers height from boiling point of a liquid versus pressure; not the aneroid or radio instrument used in aviation.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of altimeter this model covers, and on what evidence? provenance
Sources
- Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25 series), Flight Instruments chapter - Pressure-altimeter principle, Kollsman setting, indicated/true/absolute/pressure/density altitude, static-system errors, and cockpit use.
- Altimeter - Instrument kinds (pressure, radio, GNSS, laser), operational context, and common neighbouring instruments.
- Radar altimeter - Radio/radar altimeter band, height-above-ground role, and civil low-range use on approach.
- Annex 6 to the Convention on International Civil Aviation - Operation of Aircraft - Carriage and operational use of pressure and radio altimeters, altimeter-setting procedures, and height/altitude minima.
- TSO-C10 - Pressure Altimeter System - U.S. technical standard order that qualifies civil pressure-altimeter equipment.
What the second pass must settle
- Does the registry intend this entry to cover satellite-derived altitude functions and software-only displays as well as dedicated physical altimeters?
- Which authoritative device manuals should establish the measurement principles, controls and limits represented by this model?
- Should pressure references, geodetic datums and surface-relative heights be expressed through a shared neighbouring reference model?
- Which intended uses require additional acceptance criteria or service rules, and which sources establish those requirements?
- How should hybrid altimeters expose source switching, combined uncertainty and disagreements between their altitude inputs?