EXECUTIVE SUMMARY
The present Comprehensive Global Assessment on Weather Risks and Impact on Delays is the second deliverable of WP 2.1. It contains an update of existing knowledge on the identification of adverse weather, the assessment of weather impact areas in aviation operations and methods to assess the weather impact on aviation operation efficiency.

Chapter 3 describes in detail the various atmospheric hazards, which pose risks to aircraft. They include the phenomena related to thunderstorms (Cb) like lightning, microbursts/downbursts, convective turbulence, icing and also visibility. CAT, which is turbulence found in the cloud-free atmosphere, often in the vicinity of jet streams, can also be induced by thunderstorms. Depending on the severity, these hazards can lead to fatal accidents and have done so in the past. Loss of orientation
caused by low visibility especially, the prime cause for CFIT, is a serious threat.
Another hazard, caused by aircraft themselves, is wake vortices, which form at the wings of an aircraft and persist for several minutes. They can be so strong that smaller aircraft following a larger one can get into serious difficulties, sometimes resulting in loss of control. This is especially true during take-off, when the aircraft speed is low.

Volcanic ash is another phenomenon that can become hazardous for aircraft. The intake of air containing ash particles can lead to flame-out and prevent the engines from being restarted. In the past several near accidents occurred where the crew was able to recover the aircraft just in time to prevent ground collision.
For many of the aforementioned hazards, climatologies, some global, some for Europe and North America, are presented.
Additionally, simulations of wake vortex encounters and an assessment on the frequency of such events in European air traffic are performed. This includes the estimation of a quantitative measure to evaluate the effect of a WV-encounter on passengers and crew.

In Chapter 4, the global accident and incident analysis is performed. It starts with a thorough description of the ICAO-database and the methods to evaluate the latter. It is continued with the analysis of a worldwide set of accidents with respect to different types of aircraft, flight phases, weather phenomena and injuries. Additionally, chapters are included which focus on lightning strikes to aircraft and helicopter accidents. The Chapter then closes with a assessment of weather related accidents with respect to other causes.

In Chapter 5, evaluation methods to determine the weather impact on aviation delays and punctuality are described. Monitoring tools for delay are shown and discussed. As an example, the monitoring tool “Netline”, used by Tyrolean Airways, is described in more detail. The chapter closes with a listing of available delay statistics and datasets that can potentially be used for further investigations.

Chapter 6 is dedicated to weather impact studies with regard to efficiency. First, a general introduction on the effect of weather on aviation operation efficiency is given. This introduction is followed by an analysis of the impact of weather on delays, air traffic operations and ATC and an analysis of the decision-making due to the impact of weather.

The next section of Chapter 6 is an overview of available weather impact studies with regard to efficiency and includes studies on the cost of delays. Many of the studies are from the U.S. but they also give valuable information for the European air traffic system. All impact studies clearly show that there is a need for improved weather forecasts and new products as there is a great weather impact on aviation. For example, Lindsey (1998) found that 40-65% of delays that U.S. domestic airlines experience are attributable to adverse weather.

The chapter continues with an investigation of the cost benefit of new or potentially new products. A more detailed description is given of the Integrated Terminal Weather System (ITWS) and the Corridor Integrated Weather System (CIWS) as they represent major new products within the U.S. aviation system. Their benefits have already been investigated with respect to costs and safety for several locations and are described. ITWS and CIWS proved high yearly economic benefits. Furthermore, they have become valuable decision aids and have helped significantly to optimise ATC and airport authorities operations and thus also to reduce delays.
The section “Partner Delay Studies” comprises all delay studies done within FLYSAFE. A punctuality model is introduced and results from three different questionnaires, dedicated to helicopter operations, business jet operations and ATC/ATM/airport operators are presented. Chapter 6 finishes with a study on the potential of delay measures as safety metrics.

A discussion and summary is given in Chapter 7. It includes sections on all-weather operations, weather in relation to other causes and trends and recommendations.

For further information please contact:
Mr. Michael Theusner: flysafe@muk.uni-hannover.de