Clean take-offs, Spotless landings
The airside forms the core of an airport’s infrastructure since it includes the runway, taxiway, apron and stands. Cleaning of the airside is a specialised activity since it is directly responsible for the safety of the aircraft, crew and passengers. It requires trained manpower as well as equipment specialised for different applications.
Primarily, runway cleaning deals with removal of FOD (Foreign Object Debris). FOD include objects like stones, metal particles, wire, ice, birds, animal waste etc, which are not desirable and can cause tyre burst or even engine failure during an aircraft’s take-off or landing. There are several incidents where invaluable lives and property worth millions have been lost due to FOD. For example, the International Aviation News had reported an accident involving an Air France Concorde near Paris that killed 113 people in July 2000. Debris on the runway from a previous departure was held responsible for the accident in the report by French air accident investigators. This is just one example but it is an eye opener establishing the necessity for FOD removal. Worldwide companies spend US$ 6 billion for the damages caused to aircrafts and airport infrastructure in a year.
Mechanised Vs manual
Sweeping and maintenance of runways if carried out manually results not only in high operational cost, but also exposes the cleaning crew to occupational health hazards. It can also tamper with the runway surface, which is hazardous for the aircraft. Moreover, the growing aircraft traffic cannot accommodate the tedious manual cleaning process as it affects the entire operation. The problem is further augmented during monsoon and winter seasons. It is, therefore, recommended, that runway cleaning be mechanised to increase the speed and effectiveness.
The most significant reason to be concerned about the build up of rubber deposits is safety. Due to rubber deposits, an airport with large jet aircrafts will eventually have a deterioration of the pavement skid-resistance or a reduction in friction coefficients. This makes it difficult for aircraft tyres to get a grip and safely stop the aircraft. In fact, a key reason of ground-based accidents is a runoff event. When an aircraft skids off of the runway for any reason, the pavement surface will be carefully examined as a contributing factor.
When a friction test identifies a pavement surface with inadequate friction characteristics, the cause, such as rubber accumulation, is often obvious.
A friction test involves a vehicle-mounted system equipped with a computer to record the data, a measuring device to accurately record distances travelled, a tread less tyre of specific size and air pressure and a spray of metered water in advance of the “drag” wheel to simulate wet pavement, conditions under which friction readings would be the worst. The drag wheel mechanism can be mounted internally in the vehicle.
The test is taken on a non-contaminated surface to get a base reading for the “clean” pavement. Then readings are taken in the landing area, or touchdown zone. The touchdown zone measurement must be at least 80% the value of the clean pavement to be considered having a sufficient friction coefficient.
If the measurement falls below the 80% value, then the cause must be determined and measures must be taken to restore the friction coefficient to acceptable levels. The most common cause is rubber accumulation. However, it is easy to recognise, simple to correct and relatively inexpensive.
S Harikumar is AVP-LSD, Kam-Avida Enviro Engineers (P) Ltd