Altimetry Flashcards
What is the difference between altitude, height and flight level?
Altitude is the vertical distance of a level, a point or an object considered as a point, measured from mean sea level.
Height is measured from a specified datum.
Flight levels are surfaces of constant atmospheric pressure related to a specified pressure datum, 1013.2 hPa (29.92 inches), and are separated by specific pressure intervals.
The altimeter will indicate an altitude when QNH or RPS is set, a height when QFE is set and a flight level when the SAS is set.
What is the difference between elevation and aerodrome elevation?
Elevation is the vertical distance of a point or level, on or affixed to the surface of the earth, measured from sea level.
Aerodrome elevation is the elevation of the highest point on the landing area.
Describe QFE and how it is used.
QFE is the corrected barometric pressure for a specified datum. When QFE is set on an altimeter subscale, the altimeter will indicate the vertical distance, relative to the QFE datum (height). QFE is used by British Service ac when landing and taking off or flying in the visual circuit, as follows:
a. On airfields without a designated runway, the QFE datum for all procedures should be the airfield elevation (Airfield QFE).
b. In all other circumstances, the QFE datum for all procedures should be the touchdown zone elevation (Runway QFE) for the runway in use. When more than one runway is in use for simultaneous instrument and visual procedures, the QFE relevant to the instrument runway is to be used. The mixed use of QFE is not permitted.
What is the Touch Down Zone?
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What is Touch Down Zone Elevation?
The Touch Down Zone is the portion of a runway, beyond the threshold, where it is intended landing ac first contact the runway.
Touch Down Zone Elevation is the highest runway centreline elevation in the touch down zone.
What is Standard Altimeter Setting and explain its use?
Standard Altimeter Setting assumes a mean sea level pressure of 1013.2 hPa (29.92 inches). It is used for all flying above the transition altitude and when flying above 3000 ft amsl in the UK outside CAS, except when:
a. Flying in conformity with instructions given by ATC, HM Ships or an ASACS radar unit.
b. Completing manoeuvres requiring rapid changes of altitude or heading (e.g. aerobatics, spinning and air combat training).
What is Aerodrome QNH and explain when it is used?
Aerodrome QNH is the observed pressure at an aerodrome elevation corrected for temperature and reduced to mean sea level, using the ICAO formula.
When Aerodrome QNH is passed to ac, the message should include aerodrome elevation or touchdown/threshold elevation as determined by local orders. When aerodrome QNH is set on an altimeter subscale, the altimeter will indicate the vertical distance relative to mean sea level (altitude). QNH is used:
a. For calculating the Transition Level in the vicinity of an airfield.
b. For calculating Minimum Safe Flight Levels.
c. For flights in the vicinity of some civil aerodromes, although QFE is normally used for landing.
d. As a landing datum for some foreign and civil ac.
e. On request, it may be passed to military pilots for internal use within the ac.
What is Regional Pressure Setting and state its use?
RPS is the lowest forecast QNH within a designated altimeter setting region.
It is used as an altitude pressure datum for ac flying at or below the transition altitude away from the aerodrome circuit and approach patterns.
It is available hourly for the period H+0 to H+1 and ATC units should maintain a record of the current pressure settings for their local and adjoining regions. The pressure value for the period H+1 to H+2 is available on request from the Meteorological Office.
The RPS is also used to calculate the MSFL for en-route flying. When RPS is set on an altimeter subscale, the altimeter will indicate the vertical distance relative to the RPS datum (altitude).
What is Landing Altimeter Setting (QNE)?
QNE is the indication that an altimeter will give on landing when the sub-scale is set to 1013.2 hPa.
QNE information may be used by pilots of ac whose altimeters cannot be set to below 950 hPa.
What is Force QNH?
Force QNH is the lowest QNH forecast for an Operation/Exercise area for a defined time-period.
It is calculated by a suitably qualified MetO/Forecaster and promulgated to all participating units as directed by the Airspace Control Authority (ACA).
The Force QNH area can contain more than one RPS area, bisect others or be a portion thereof: hence discrepancies between Force QNH and RPS can be apparent.
Therefore, the area within which the Force QNH will be utilised should be clearly defined in appropriate Op/Ex Orders (e.g. ACO/SPINS/ACN).
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