Pratt & Whitney examining excessive heating of A320 Neo engines

The issue led to smoke engulfing the cabin of IndiGo aircraft last week leading to emergency landing by the pilot

Engine maker Pratt & Whitney is investigating incidents of excessive heating of the compressor seals in the Airbus A320 Neo planes leading to its failure- the latest in a series of problems that have plagued the new turbine, according to Indian aviation regulator Directorate General of Civil Aviation.

The problem was identified while investigating the incident where thick smoke had engulfed the cockpit and cabin of an IndiGo aircraft forcingthe pilot to do an emergency landing and evacuation of passengers at Kolkata last week.

The problem though reported in very few isolated incidents is a cause of concern for the engine maker as the current model of seal- the dry face carbon seal was introduced by the company as a replacement after a problem with the knife edge compressor seal led to engine failure due to which the IndiGo and Go Air had to ground around 14 aircraft earlier this year.

The modified knife-edge seal introduced by P&W in late 2017 started showing signs of wear in the early cycle of its life. The broken seal started damaging the compressor and turbine, causing in flight shutdowns following which Pratt started retrofitting engines with dry face carbon seal.

The scale of the latest problem appears less disruptive than recent issues with the engine’s combustor, oil seal and knife-edge seal. “As of now very few such incidents have been reported and Pratt is working on a solution,” DGCA head BS Bhullar said.

Preliminary investigation of the incident by the engine maker has found that the temperature of the rear end of the dry face seal is increasing more than the front end as it is not getting lubricated adequately. So, Pratt is working on a modification of the seal which would increase the flow of oil leading to higher lubrication in the rear end of the engine. The new design will be released to operators only in early 2019, a person aware of the development said.

Till the new design is introduced, the US-based engine manufacturer as a temporary measure has released a software to operators which cools down the temperature of the turbine by almost 40 degrees celsius.

“Pratt & Whitney is investigating the cause of the problem. As temporary measure, they have released a software which bring the temperature down by almost 40 degrees celsius helping to mitigate such problem. IndiGo and Go Air are retrofitting their engines with this software,” Bhullar said.

“Cases of engine failure after the introduction of dry face seal have reduced significantly, but there are issues since it’s a new project and Pratt is working to find the solution,” said a person aware of the development.

The geared turbofan, a step-change in the efficiency of turbines for commercial aircraft, has been hit by a slew of design flaws that have grounded planes, delayed deliveries and prompted millions of dollars in compensation claims.

In 2016, initially the aircraft started reporting oil metal detector warnings.

The third engine bearing compartment had a seal which didn’t work correctly at high flight levels.

The thin air caused the air riding seal members to sometimes oscillate.

This left metal particles in the engine oil, which gave warnings, pointing to a potential engine problem.

The manufacturer did a fix which was a change to a more classical carbon seal.

The third problem was combustion chamber linings which had unforeseen hot spots, reducing the operational life. The fix provided was a combustion chamber with more pores which can provide more cooling.