3. 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, 1013.25 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 AS when landing and taking off or flying in the visual circuit, as follows:
a. On an Aerodrome 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 for the runway in use (Runway QFE). 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:
a. Touch Down Zone Elevation?
b. Touch Down Zone?
a. Touch Down Zone Elevation is the highest runway centreline elevation in the touch down zone.
b. Touch Down Zone is the portion of a runway, beyond the threshold, where it is intended landing aeroplanes first contact the runway.
What is Standard Altimeter Setting and explain its use?
Standard Altimeter Setting assumes a mean sea level pressure of 1013.25 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 Air Surveillance and Control System 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 International Civil Aviation Organization (ICAO) formula. When Aerodrome QNH is passed to aircraft, the message will 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). Examples of where Aerodrome QNH can be used include:
a. For calculating the TL in the vicinity of an airfield.
b. For calculating Minimum Safe Flight Levels (MSFLs).
c. As a landing datum for some foreign and civil aircraft.
d. For flights arriving, departing or flying in the vicinity of civil aerodromes.
e. For internal use within an AS when requested by military aircrew.
What is Regional Pressure Setting and state its use?
The RPS is the lowest forecast QNH within a designated altimeter setting region, and is used as an altitude pressure datum for AS flying at or below the Transition Altitude (TA), away from aerodrome circuit and approach patterns. It is available hourly for the period H+0 to H+1 and ATC units will maintain a record of the current pressure setting for their local and adjoining regions. The 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 sub-scale, 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 1013.25 hPa. QNE information may be used by pilots of AS whose altimeters cannot be set to below 950 hPa. A QFE/QNE conversion table should be held by ATC for use in such circumstances.
How is Force QNH used?
When controlling AS within a defined Operational/Exercise (Op/Ex) area, controllers should use the Force QNH as defined in the relevant Op/Ex Order.
a. Where appropriate for the general conduct of the Op/Ex, Force QNH should be used at all times whilst clear of non-segregated Controlled Airspace (CAS). However, if a Force QNH is required for lower level flight, but airspace structure dictates that flight on Standard Altimeter Setting (SAS) at higher altitudes is also necessary, a ‘Force Transition Altitude and Level’ (providing adequate terrain and airspace separation) should be set and promulgated within the same Op/Ex Orders.
b. Validity of Force QNH should be for as long a period of time as possible (up to 6-hr periods), preferably covering likely flying waves. As a minimum, and only for Operations with a C2 agency in communication with all participants, Force QNH should be issued and promulgated at least an hour in advance, valid for one hour (akin to current Regional Pressure Setting (RPS) procedures).
c. Force QNH should be promulgated through Met Office channels as agreed by Op/Ex planners.
