“So we had the choice of going in and making the modification, or continuing with the test. . . We elected not to make the modification because we didn't want to lose schedule. [But], we had a unique way of monitoring which uses pressure measurements to get a feel for how the part has changed over the testing,” says Saia.
“We completely ran the fan, LP compressor and LP turbine as expected except for one point—the overtemp test.” This runs the engine 300-400F above red line and—relative to the highest expected thrust rating of 33,000 lb. for the engine on the A321—is equivalent to about 39,000 lb., or 20% more thrust.
“We decided we'd leave it for the last test in case there was any distress. . . .When we were done, we had distress on the vane well beyond what was operationally acceptable. We had notified Airbus [of the schedule risk of] some vane damage—but it was a conscious decision.”
In the meantime, modifications were made to engine No. 3, the HP system stress test unit next in line. “We were able to make the modification before we went to test. It took us a couple of weeks to validate the root cause and identify corrective actions. It was quite simple, we just added a few cooling holes at the root of the vane.” Rather than use extra cooling air, Saia explains, the existing air is redistributed.
“We ran No. 3 at 5% above rotor red line and successfully demonstrated it.” Pratt classes the event as a success for the Block 1 phase as it unearthed the need for a revision before it reached the final certification standard stage. “We go into a test not wanting to over-cool a part. You want to do enough to let it live in the environment, but nothing more,” Saia adds.
One of the earliest to begin the next phase is engine No. 5, the first Block 2 unit now under assembly. “It will go to test in early October but is still on its schedule,” insists Saia. The program includes margin for a break between Blocks 1 and 2. “We know we are going to find areas to modify, and that certification testing will start in October and go through June 2014. We deliver engines to Airbus late in June or early July .”