IN-DEPTH tests carried out in the wake of the fatal Clutha helicopter crash have been explained to a court as relatives of those who died listened.

Evidence has been led today on the eighth day of the Clutha Fatal Accident Inquiry (FAI) from aerospace engineer Holger Mendick, of Airbus Helicopters.

The compliance verification engineer for fuel systems, who has flown from Germany for the inquiry, is today continuing to give evidence.

Yesterday Procurator Fiscal Depute Sean Smith took Mr Mendick through a report from April 21, 2015, which looked at water contamination in the helicopter's fuel transfer system.

Read more: German aeronautical engineer to give evidence

The 44-year-old told the court of the various ways the fuel system of an EC135 helicopter could become contaminated with water.

Tests aimed to see if water in the fuel system would have any impact on the fuel level sensors.

Engineers injected water directly into the tank in a process the court heard is called "accelerated testing."

"Free water in the fuel system is not seen as a problem," Mr Mendick told the court.

"Water contamination may only influence the fuel level sensors when it is mixed with fuel to form an emulsion."

Airbus engineers developed a presentation on the EC135 helicopter's fuel system in January 2014 to explain how water contamination may occur after an engine compressor wash.

During investigations two root causes of water entering the fuel tank were found.

A service bulletin was also released in 2014 to explain that the drain line in the fuel tank had been moved to a higher point on the system's drain bottle to avoid water being sucked back in to the tank.

In 2009 Airbus, the court heard, had said it would retrofit fuel sensors in the EC135 helicopters.

A report said: "The fuel flow sensor indicates the current fuel flow consumption and the remaining flight time can be indicated."

This sensor is not standard on helicopters, Mr Mendick said, and the Clutha helicopter - G-SPAO - did not have one.

Read more: Day six of the inquiry hears from air traffic controller

The inquiry has previously heard that the Police Scotland helicopter had five low fuel warnings before both engines flamed out and it crashed.

The helicopter, which came down on the roof of the Clutha Vaults on November 29, 2013, was found, according to the Airbus report, to have a"total absence" of water in its fuel tanks.

The court also heard that the pitch of the helicopter can effect how much fuel is in the tanks, with the pitch causing spillage of fuel between tanks.

After around three hours of questioning, Mr Smith told the court that a theory suggesting fuel emulsification caused the helicopter's fuel sensor to give an inaccurate reading could be counted out as no water had been found in the aircraft's tanks.

Another suggested scenario was that water may have built up between the fuel sensor's concentric tubes over several flights.

This would have been able to cause a fuel over-reading that would have been there before the helicopter's fatal last flight.

The court did not rule out this theory.

Another suggestion, which was ruled out, was that a single droplet of water in the fuel sensor could have short-circuited the fuel sensor tubes.

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But the court heard the fuel quantity fail caption did not come on in the cockpit, allowing the theory to be discounted.

Pilot David Traill, 51; PC Tony Collins, 43; and PC Kirsty Nelis, 36, died along with seven customers who were in the bar, Gary Arthur, 48; Joe Cusker, 59; Colin Gibson, 33; Robert Jenkins, 61; John McGarrigle, 58; Samuel McGhee, 56; and Mark O'Prey, 44.