The 135 air inlet design is a throwback to the 105.
It does have its failings -
The engines breath from the space where the TRDS passes between the engines.
The downside is that any wayward ty-wrap, lost split pin or lock wire that is misplaced on the XMSN deck will go through the engine.
Maintenance techs need to be extremely vigilant that nothing is left on the transmission deck as it is all part of the engine inlet!!!
In reality the engines actually breath around the mast opening. As any dust or dirt recirculates toward the mast it also goes straight through the engines.
The old particle separator had a seal in this area that never really worked that well.
The later models have a barrier filter available as seen in the pic of the T3/P3. The inlet in this area is standard for a T3/P3 with or without IBF.
On the IBF equipped and/or T3/P3 the engine oil cooler exit duct is moved to the upper part of the cowling so that the engine does not re-ingest hot air.
