Pratt & Whitney says a minor cooling system redesign of its PW1100G geared turbofan to counter thermal “distress” in a nozzle guide vane will not impact the start of test flights of the Airbus A320NEO in late 2014.

According to a Reuters report, Pratt uncovered the issue in a high pressure turbine nozzle guide vane during stress tests of an endurance engine in May.

Pratt and Airbus both insist the issue will not delay the flight test and certification program, which is due to culminate with first deliveries of the initial PW1100G-powered A320NEO in October 2015.

Although the cooling revision is typical of the design adjustments made as a result of tests during the initial phases of an engine development program, the fiercely contested battle with CFM’s competing Leap-1A over the A320NEO raises the profile of every incident and discovery.

While Pratt is downplaying the event there is speculation over how much additional cooling air is being taken from the cycle by the redesign, and whether this may have some effect on overall performance.

In its comments to Reuters, Pratt insists there is no impact on either fuel burn or schedule.

Fuel efficiency is one of the key drivers in the contest between the two NEO engine contenders. According to figures from the engine makers and Airbus, the competition over the A320NEO is finely poised with CFM slightly ahead. The Leap-1A has been selected for just over 800 A320NEO family aircraft, or around 34% of the firm aircraft orders.

The PW1100G has been selected for around 750 aircraft, or 32%, while engines have yet to be selected for a further 800 A320NEOs on firm order.

The first of four ‘block 1’ test engines, rated at 33,000lb thrust, began running at Pratt’s West Palm Beach, Fla. test site in early December. By late May four engines were on test with a fifth engine expected to join the test program in September.

This will be the first of four ‘block 2’ standard engines that will be used for Part 33 certification.

Test work will focus on specific systems for certification and will include more critical evaluations such as bird strike and fan blade off.