Section 1, Chapter 7 - Altimeter Setting & Vertical Reference Flashcards
What are the notified units of pressure for flying within UK airspace, and how are pressure settings in inches of mercury handled?
Hectopascals are the notified units for pressure measurements within UK airspace. Pilots are expected to convert from hectopascals to inches of mercury if necessary. Controllers will only provide pressure settings in inches of mercury when specifically requested by an individual aircraft. A conversion table is available in Appendix A.
How are Flight Levels measured and separated in UK airspace?
Flight Levels are measured with reference to the standard pressure setting of 1013.25 hPa. IFR cruising flight levels above the transition altitude are separated by pressure intervals corresponding to 1,000 ft up to FL410 and by 2,000 ft above FL410 in the International Standard Atmosphere (ISA).
What do QNH and QFE altimeter settings indicate, and how are these settings provided to pilots?
- QNH altimeter setting: Indicates altitude.
- QFE altimeter setting: Indicates height above the reference datum.
- Both settings are rounded down to the nearest whole Hectopascal before being passed to the pilot.
- Settings can be provided to the nearest tenth of a Hectopascal if requested.
What is the purpose of the Regional Pressure Setting (RPS) and how should it be used?
- Purpose of RPS: A conservative forecast of the lowest QNH value within an altimeter setting region (ASR) to mitigate the risk of controlled flight into terrain (CFIT), though it can increase the risk of vertical airspace infringement.
- Availability: Provided hourly for the period H+1 to H+2 in whole Hectopascals.
- Usage:
1. ATSUs must have the RPS for their ASR and adjacent regions, providing these values to pilots upon request or at the controller’s discretion.
2. RPS should not be volunteered if not appropriate for the flight, especially for aircraft operating below controlled airspace as per AIP ENR 1.7 paragraph 3.9.
3. For airspace below TMAs and CTAs listed in ENR 1.7 paragraph 3.9, the QNH of an adjacent aerodrome should be used instead of the RPS for aircraft at or below the Transition Altitude.
What is the transition altitude and what is the common value for civil aerodromes?
The transition altitude is the altitude at or below which the vertical position of an aircraft is controlled by reference to altitude (or height when QFE is used). Wherever possible, there is a common transition altitude for aerodromes within a control zone. Unless otherwise notified, the transition altitude for civil aerodromes is 3,000 ft.
What is the transition level and how is it determined within and outside controlled airspace?
The transition level is the lowest Flight Level available for use above the transition altitude, ensuring at least a nominal 1,000 ft separation. It is determined as follows:
- Within controlled airspace: By the controlling authority, based on the QNH of the major aerodrome.
- Outside controlled airspace: By the Aerodrome Operator, based on the aerodrome QNH.
A table in Appendix A provides further details for calculating the transition level.
What is the transition layer and how is it defined in the UK?
The transition layer is the airspace between the transition altitude and the transition level. In the UK, the first available flight level above the transition altitude is separated from the transition altitude by a minimum pressure interval corresponding to a nominal 1,000 ft.
How should pilots assess vertical position and what must controllers ensure when issuing pressure settings?
Pilots normally assess vertical position using an accurately set altimeter. Controllers must:
- Always issue the correct pressure setting.
- Check the read-back from the pilot.
- Clearly specify the unit of measurement for altimeter settings below 1000 hPa and carefully verify the read-back.
Altimeter Subscale Settings and Reporting:
1013.2 hPa (Flight level):
- At or above the transition level.
- Climbing through the transition layer.
- Above 3,000 ft amsl, not near an aerodrome.
QNH (Altitude):
- At or below the transition altitude (near an aerodrome or under specified TMAs/CTAs).
- Descending through the transition layer.
- During final approach.
QFE (Height):
- During final approach, as required by local procedures or pilot request.
Regional Pressure Setting (RPS) (Altitude):
- At or below 3,000 ft amsl outside controlled airspace and not near an aerodrome.
- Note: When climbing from an altitude to a Flight Level, vertical position reports in terms of Flight Level unless ATC requests intermediate altitude reports. For descent, pilots switch to QNH after the final Flight Level vacating report unless further Flight Level reports are requested.
What is aerodrome elevation and how are QFE aerodrome and QFE threshold settings used?
Aerodrome Elevation: The elevation of the highest point on the landing area, used as the reference for visual manoeuvring (circling) heights. Each runway also has a published threshold elevation.
QFE Settings:
* QFE Aerodrome: Pressure setting associated with the aerodrome elevation.
* QFE Threshold: Pressure setting associated with the threshold elevation, used when the threshold elevation is 7 ft or more below the aerodrome elevation.
What information should be given to aircraft prior to taking off?
Prior to taking off, aircraft should be given the aerodrome QNH. The transition altitude and level will only be provided if requested by the pilot.
What altimeter setting and additional information should be provided to arriving aircraft?
- Aircraft at or below the transition level are to be given the aerodrome QNH.
- When cleared to descend from a Flight Level to an altitude, include the appropriate QNH in the same transmission. Include requests for Flight Level vacating reports with the descent clearance.
- The transition level must be communicated to the pilot in due time before their aircraft reaches it during descent via voice communications, ATIS broadcast, or data link.
- After QNH is set by an aircraft, all references to vertical position shall be in terms of altitude. Vacating reports, if not requested during descent clearance, may be in terms of altitude, especially if the aircraft has only one altimeter.
- Provide the appropriate QNH before an aircraft commences an approach.
- Aerodrome and threshold elevations should be available upon request. Provide the appropriate QFE if requested by the pilot or if local procedures require it.
- After a missed approach, refer to vertical position in terms of altitude and include QNH with the subsequent clearance if necessary.
What altimeter setting should be provided if an aircraft makes an instrument approach followed by a visual manoeuvre (circling) to land on another runway?
If an aircraft makes an instrument approach followed by a visual manoeuvre (circling) to land on another runway, the appropriate QFE aerodrome or QFE threshold should be given.
How are the lowest cruising levels determined and assigned on ATS routes?
- Cruising levels on ATS routes are notified in the UK AIP at ENR 3. The lower Flight Levels may not always be available due to variations in atmospheric pressure.
- The lowest cruising level available for assignment is determined at the ACC using the appropriate Regional Pressure Setting and must always be at least 500 ft above the notified base on an ATS route.
- Unit procedures for determining and using the first available Flight Level above the transition altitude are described in MATS Part 2.
What vertical separation should controllers maintain when allocating levels to aircraft in relation to the limits of controlled airspace?
Controllers should not allocate a level to an aircraft that provides less than 500 ft vertical separation above the lower limit of a control area (including TMAs and ATS routes) or below the upper limit of a control zone or control area (including TMAs) where Class G airspace adjoins vertically, except when aircraft are leaving controlled airspace by descent or climb. This ensures vertical separation from aircraft operating at the limits of controlled airspace.
