Monday, April 25, 2016

The 787 GE Pip II Engine Ices.

Waiting until the press storm ceases on the GE engine icing found on half the flying 787 flying has been a tedious read. I found one article that articulated the problem where the other 99% of the articles were touting the FAA pronouncement. 

Ainonline photo 2012  GEnex 1B-Pip II

However, the fix was in before the FAA declared the urgency to fix. Boeing had already pushed GE towards making the engine flaw safe. As is understood by Winging IT, engine icing occurs with the PIP II GE 787 engines, because of fan blade clearance from its engine housing by about a 1/10th of an inch around its circumference. The fix already started before FAA issued its latest engine demand had been installed on about fifty aircraft. 

Photo by Aviexmax:  Note the black and silver fan blade almost touches inside diameter wall. FAA directive increases housing diameter by fractions of an inch, allowing a larger blade tip to wall gap which will prevent any known icing.

It is presumed, this fix is for widening the tolerance by greater than 1/10th of an inch, mitigates any future icing situations. The current internal procedure is for the pilot to administer thrust increases every five minutes and blasting out any ice build up until the "Blade Gap" is open. The technical fix is for making a larger gap which would diminish performance somewhat, but eliminate the occurrence of ice buildup entirely.

The fear is an obvious potential for a two engine shutdown placing a real and imminent danger under certain conditions. Even one occurrence of a two engine 787 shutdown from icing, is catastrophic for everyone, so the FAA has pushed out an "all hands on deck" call (bulletin)  for fixing this problem. Everyone is now aware, and every aviation 787 customer with PIPII engines is demanded by the FAA for making a remedial fix by expanding the blade gap from the engine wall at a prescribed safe distance. The time slot for this level of urgency is about 120 days from now. This time allotment for a fix suggests the 787/GE engine is sound, but has a critical weakness under random conditions which raises the risk bar too high for the flying public.

The solution can be completed by two methods. 

·      The ready solution is mounting at least one PIP I engine type out of two engines on a 787.
·      The second solution requires grinding down the engine opening casement to recommended "fix" diameter, giving the blade clearance and ample space for not allowing any ice build-up.

The "fix" will affect overall fuel performance by a small margin. The problem could have not been prevented from the usual testing regimen, but any future engine development will of course test specifically for this condition when finding the optimal performance package for this type of design. The FAA's due diligence after an incidence is what matters for all the people using, building and designing aviation as it advances. Thank you FAA!!