0 METWSG1IP4 METWSG1IP5 211107 METEOROLOGICAL WARNINGS STUDY GROUP (METWSG)

A USER POINT OF VIEW ON LOW LEVEL TEMPERATURE INVERSIONS

METWSG/1-IP/4

METWSG/1-IP/5

21/11/07

METEOROLOGICAL WARNINGS STUDY GROUP (METWSG)

FIRST MEETING

Montréal, 20 to 22 November 2007

Agenda Item	7:	Amendments to provisions related to wind shear warnings and alerts
	7.3:	Consider the need to provide information on low-level temperature inversion either in a specific warning or in the supplementary information appended to local reports and METAR/SPECI

A user point of view on Low Level Temperature Inversions

(Presented by Mr. Hervé Fournerat)

SUMMARY

This paper presents information on a user point of view on low level temperature inversions

INTRODUCTION
1. Low level temperature inversions (LLTI) have a detrimental effect on:

aircraft performance during initial climb after take-off or rejected landing; and
aircraft handling and auto-pilot/auto-throttle behaviour during final approach.

When climbing through a temperature inversion, two factors will adversely affect the performance of an aircraft:

lower air density will result in lower indicated airspeed, requiring the pilot to reduce the climb path angle to regain his speed; and
higher temperature will reduce engine performance. For a modern twin-engine jet aircraft departing at its maximum “2nd segment” take-off weight, we can estimate that a 15° increase in temperature will reduce the resulting climb path angle by up to 30 per cent (angle of 1.6 per cent instead of 2.4 per cent).

During landing, sudden increase in both airspeed and engine thrust might lead to unstabilized approach, or long landing and runway excursions.
These effects of LLTI have been presented by IFALPA at the METG/16, and the EANPG subsequently agreed on the need to report such phenomena.
Although LLTI might occasionally be associated with wind shear, they often appear in stable air mass. Some of the findings in SN/08 relating LLTI to wind shear are therefore considered inappropriate by IFALPA.
Evolution of LLTI phenomena is usually slow, especially compared to wind shear. Therefore, a specific warning might be considered unnecessary, and IFALPA proposes that:

Annex 3 should include a definition of LLTI;
LLTI should be included in the supplementary information appended to local reports and METAR/SPECI; and
LLTI should be reported in ATIS – ref. Annex 11, para. 4.3.7 s), 4.3.8 s) and 4.3.9 r).

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