Aircraft Operations

II-4-1-2
Procedures — Aircraft Operations — Volume I
1.2.2 Atmospheric effects
1.2.2.1 Atmospheric errors associated with non-standard temperatures are considered in the design of the
approach obstacle clearance surface. When temperatures are lower than standard, the aircraft’s true altitude will be
lower than its barometric indicated altitudes.
1.2.2.2 Most existing VNAV systems do not correct for non-standard temperatures. At temperatures below
standard, these errors can be significant and increase in magnitude as altitude above the station increases. The gradient
of the approach obstacle clearance surface is reduced as a function of the minimum temperature promulgated for the
procedure.
Note.— International Standard Atmosphere (ISA) temperature is 15°C at sea level with a lapse rate of 2°C per
1 000 ft of altitude.
1.2.3 Along-track position uncertainty
All RNAV systems have some amount of along-track error. This along-track uncertainty can mean that the VNAV
system will start the descent too early and result in an error in the vertical path. This is compensated for in procedure
design by relocating the threshold level origin of the approach obstacle clearance surface.
1.2.4 Flight technical error (FTE)
Flight technical error (FTE) is assumed to be contained within the standard non-precision margin of 75 m (246 ft). This
is added below the VPA before the obstacle clearance surface is adjusted for cold temperature and along-track error.
1.2.5 Other system errors
Other errors include static source error, non-homogenous weather phenomena and latency effects. These are
insignificant compared with the other errors already addressed and are considered as contained within the existing
margin.
1.2.6 Blunder errors
Application of an incorrect or out-of-date altimeter setting, either by air traffic control or the pilot, is possible and must
be prevented by appropriate operational techniques.
1.3 EQUIPMENT REQUIREMENTS
1.3.1 APV/baro-VNAV procedures are intended for use by aircraft equipped with flight management systems
(FMS) or other RNAV systems capable of computing barometric VNAV paths and displaying the relevant deviations
on the instrument display.
1.3.2 Aircraft equipped with APV/baro-VNAV systems that have been approved by the State of the Operator for
the appropriate level of lateral navigation (LNAV)/VNAV operations may use these systems to carry out APV/baro-
VNAV approaches provided that:
23/11/06