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There has been at least one occasion on which an aircraft ran out of fuel due
to an error in converting between kilograms and pounds. In this particular
case the flight crew managed to glide to a nearby runway and land safely (the
runway was one of two at a former airport then being used as a dragstrip).
Many airlines request that fuel quantities be rounded to a multiple of 10 or
100 units. This can cause some interesting rounding problems, especially
when subtotals are involved. Safety issues must also be considered when
deciding whether to round up or down.
• Height units
The actual height of an aircraft is based on the use of a pressure altimeter (see flight level for
more detail). The heights quoted here are thus the nominal heights under standard
conditions of temperature and pressure rather than the actual heights. All aircraft operating
on flight levels calibrate altimeters to the same standard setting regardless of the actual sea
level pressure, so little risk of collision arises.
In most areas, height is reported as a multiple of 100 feet (30 m), i.e. A025 is nominally 2,500
feet (760 m). When cruising at higher altitudes aircraft adopt flight levels (FLs). Flight levels
are altitudes corrected and calibrated against the International Standard Atmosphere (ISA).
These are expressed as a three-figure group (e.g., FL320 is 32,000 feet (ISA)).
In most areas, the vertical separation between aircraft is either 1,000 or 2,000 feet (610 m).
In China and some neighbouring areas, height is measured in metres. The vertical separation
between aircraft is either 300 metres or 600 metres (about 1.6% less than 1,000 or 2,000 feet).
Until 1999, the vertical separation between aircraft flying at high altitudes on the same airway
was 2,000 feet (610 m).
Since then there has been a phased introduction around the world of reduced vertical
separation minimum (RVSM). This cuts the vertical separation to 1,000 feet (300 m) between
about 29,000 feet (8,800 m) and 41,000 feet (the exact limits vary slightly from place to place).
Since most jet aircraft operate between these heights, this measure effectively doubles the
available airway capacity. To use RVSM, aircraft must have certified altimeters, and autopilots
must meet more accurate standards.
A - Z of Flight
July 2017
www.alliance-airways.net
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