Slippery runway & more so the safety area at Kozhikode may be a leading cause of the Air India Express crash

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RESA  The entire state machinery is on overdrive to defend the Calicut Airport stating that it was completely safe for flight operations. There are two significant points to focus on while determining the causes of the accident.  1. Previous safety audits have pointed to vegetation on the runway end safety area (RESA). 2. The rubber deposits at the ends of the runway may have been a contributory cause of the accident. Comparison A comparison of the runway friction values indicates a possibility of higher rubber deposits or poor runway friction levels at both ends of the runways. A friction level below 0.47 requires maintenance action as per the Indian Aeronautical Information Publication. The combination of runway friction and vegetation on the RESA may have been a significant factor that may have caused the Air India Express 1344 runway overrun at Kozhikode on 7th Aug 2020. Must note that the runway has a pronounced crown close to the middle and drops more than 25 feet on either side.

Kozhikode runway friction delayed as top policy makers certify the runway safe for operations

The runway friction test is mandated by the DGCA to be carried out periodically for safe flight operations. 

A medium to big aircraft typically lands at a speed of 220-260 kmph. The primary means of stopping the aircraft is with the wheel brakes like any other vehicle. Since the runway length is limited,it is therefore important that the runway is not slippery & the wheels have a good grip on the runway by generating friction between the two surfaces.Lesser friction would mean lesser braking response. Factors that affect braking are the condition of the runway, dry/wet & rubber deposits. Each landing of the aircraft leaves behind about 700 gms of rubber from the tires due to sudden wheel spin up and this accumulates over a period of time depending on how busy the airport is.

 If the rubber is not removed periodically, the grains of the runway surface which provide the grip get filled with the rubber and they become smooth. Adding to this if there is even a film of water few millimeter deep, the aircraft is likely to slip & braking is severely impacted. If a pilot is not provided this critical information then they calculate their landing distance requirements based on the assumption that the rubber deposit & the film of water is below the danger levels. This is the reason why it is mandated to check the runway friction levels and remove rubber deposits periodically.  

RESA
RESA at Kozhikode

 

The purpose of providing RESA is to minimise damage to an aircraft undershooting & overrunning the runway. The RESA needs to be kept cleared. Vegetation on the RESA will make it slippery especially when it is raining. While it has been pointed out to the airport operator on previous occasions that the maintenance of the RESA is not as per standards, a surveillance carried out remotely ought to have checked the condition of the RESA by seeking photographic evidence. The vegetation growth as seen from the images is well developed and points out at failure of the air operators safety management system & the DGCA's oversight. On table top runways where the consequences of an overrun are severe, the checks have to be more regular and strict. The hazard identification and risk management is documented in the manuals but not implemented and enforced.

Read the blog on why investigators must focus on aquaplaning


The elevation profile will give a good picture of the undulations on the runway where more than 3mm depression will make the runway accumulate water and make it slippery.

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