Originally Posted by RANDOMPERSON8008 November 27 2021
Does anyone have any good resources to study the potential operational impacts of temperature uncompensated VNAV systems such as those used in the Boeing 747-400 and 747-8?
Found the following in,
https://www.icao.int/SAM/eDocuments/...VNAV%20eng.pdf
This essentially restates what you and others are saying but being an Advisory Circular, it provides context and guidance for VNAV with & without temperature compensation. We all know about the cold-temperature case but your post raises the high-temperature case which is rarely closely examined. But your enquiry is a good one. As "heat domes" such as the 40C to 45C temperatures last July-August experienced in the Pacific Northwest, (Washington State, British Columbia) increase, the "high temperature" case may become more relevant.
ADVISORY CIRCULAR
AC : 91-010
DATE : 12/10/09
REVIEW : 1
ISSUED BY : SRVSOP
SUBJECT: AIRCRAFT AND OPERATORS APPROVAL FOR APPROACH OPERATIONS
WITH VERTICAL GUIDANCE/BAROMETRIC VERTICAL NAVIGATION
(APV/baro-VNAV)
1. PURPOSE
This advisory circular (AC) establishes APV/baro-VNAV approval requirements (barometric vertical
navigation only) for aircraft and operators. Barometric vertical navigation may be included together with
lateral navigation in a RNP APCH approach, as established in CA 91-008. Criteria of this AC together with
criteria of AC 91-008, establish requirements for RNP APCH approach with baro-VNAV.
An operator may use alternative means of compliance, provided they are acceptable to the Civil Aviation
Administration (CAA).
Originally Posted by p.11 [b
10.3.2 Recommended functions]"a) Temperature compensation The baro-VNAV navigation system should be capable of
automatically adjusting the vertical flight path for temperature effects. The equipment should
provide the capability for entry of altimeter source temperature to compute temperature
compensation for the vertical flight path angle. The system should provide clear and distinct
indication to the flight crew of this compensation/adjustment."
and,
Originally Posted by p.14
13. TEMPERATURE LIMITATIONS
a) For aircraft using barometric vertical navigation without temperature compensation to conduct the
approach, cold temperature limits are reflected in the procedure design and identified along with
any high temperature limits on the charted procedure. Cold temperatures reduce the actual
glidepath angle, while high temperatures increase the glidepath angle. Aircraft using barometric
vertical navigation with temperature compensation or aircraft using an alternate means of vertical
guidance (e.g., satellite-based augmentation system (SBAS)) may disregard the temperature restrictions.
b) Since the temperature limits established in the charts are only assessed for obstacle clearance in
the final approach segment, and since temperature compensation only affects vertical guidance,
the pilot may need to adjust the minimum altitude on the initial and intermediate approach
segments, and at the decision altitude/height (DA/H)).
Note 1.- Temperature affects the indicated altitude. The effect is similar to having high and low pressure changes, but
not as significant as such changes. When the temperature is higher than standard (temperature under international
standard atmospheric (ISA) conditions)), the aircraft will be flying above the indicated altitude. When the temperature is
below the standard, the aircraft will be flying below the altitude indicated in the altimeter. For further information, refer to
altimetry errors in the aeronautical information manual (AIM)
Note 2.- The ISA standard conditions at sea level are:
¾ The standard temperature is defined as 15º Celsius (centigrade’s) or 288.15º Kelvin;
¾ The standard pressure is defined as 29.92126 inches of mercury (Hg) or 1013.2 hectopascals (hPa); and
¾ The standard density for these conditions is 1.225 kg/m3 or 0.002377 slugs/cubic ft. "