Impacts of Weather on Aviation Delays and Diversions at Jomo Kenyatta International Airport, Kenya

Abstract

Adverse weather is the main cause of the disruptions to operations at Jomo Kenyatta International Airport (JKIA), Kenya. In order to assess the potential implementation of a weather impact index on aviation delays at JKIA, meteorological data composed of Meteorological Aviation Reports (METARs and SPECIs) and Terminal Aerodrome Forecast (TAFs) were used in this study, and the data was gathered from KMD and JKIA. The decoding of the METAR and SPECI messages made it possible to identify the weather phenomena (causing aviation delays). The times, dates, months and year of each occurrence of aircraft delay or diversion made it easy to find the METAR or SPECI and TAF messages that were associated with the incident. The aviation weather-related delay and diversion data was gathered from KCAA. The study categorized the weather elements that occurred at JKIA from years 2000 to 2009 and examined the type of adverse weather that impacts the aviation operations in term of departure delay, arrival delay and diversion of aircraft. The need for a simplifying hypothesis for the analysis of incidents of delays and diversions led the study to operate a method of ranking the weather categories adopted. This hierarchy is important insofar as it makes it possible to assign a specific category in the specific case where several categories are coded in the same message associated with an aircraft delay or diversion. The temporal analysis in this study is composed of the annual, monthly analysis and the analysis of the 4 daily times which reflect the intensity of the airport operations that is a function of the capacity of the airport. In order to assess the Terminal Aerodrome Forecast (TAF), a TAF assessment technique was adopted. The evaluation of the TAF consists, for each unit of delay or diversion, in using the METAR which is the actual meteorological situation observed to test the accuracy of the TAF. The considered TAF is the one at least 6 hours before since this time is more than enough to allow good flight planning. ICAO regulation from Annex 3 for operationally desirable accuracy of forecasts is used for visibility, cloud amount and cloud height verification in this study. From the analysis of METARS, delay and diversion incidents, and, delay and diversion durations, it was found that the highest contributors are fog/mist, thunderstorm and low level clouds, followed by rain not originating from convective clouds and wind causing runway change. From the examination of the accuracy of the Terminal Aerodrome Forecasts (TAFs) that were associated with the delays and diversions, it was found that when the percentage of TAF accuracy is high (above 65%), decrease in delay and diversion incidents begins. Also when the percentage of TAF accuracy is beyond 67% to reach 73%, the number of delay and diversion incidents decreases and drops sharply to a small number. Therefore, improving the forecast accuracy at JKIA results in enhancing the aviation safety, in passenger satisfaction, in improving the airport capacity and in allowing an orderly flow, in avoiding and reducing the delays and diversions with effect to improve the finances of the airlines operating at JKIA. When the percentage of TAF accuracy is low (48%), the delay and diversion incidents is very high. Any slight increase in TAF accuracy vi from 48% until 65% leads to a slight decrease in combined-delay/diversion incidents. Therefore, a deterioration in TAF accuracy at JKIA results in decreasing the aviation safety, in reducing the airport capacity, in passenger inconvenience, in increasing the delay and diversion incidents with effect of income loss (due to additional costs) to the airlines operating at JKIA. The study reveals the relevance of International Civil Aviation Organization (ICAO) regulations which require 80% of forecasts to be successful. It was found that adverse weather will generate delays and diversions at JKIA despite the accuracy of a TAF, however an improved planning can reduce the duration and impact of delays. A weather impact index system for in-flight delay/diversion and combined-delay/diversion models were designed to assess weather-related risks and that can be used in estimating and planning for JKIA delays. Recommendations for delay reductions are made. Case studies show the validity of applying the developed index models in operations and its usefulness in planning and management, and therefore being proactive in aviation operations.