Engine Sync - Use or Not

[johngtatp]

I recall reading that engine sync improved passenger and crew fatigue as well as engine and airframe fatigue. Most in our flight department do not use this and I was looking for references on the subject. The autothrottles sync EPR unless otherwise selected and N1 and N2 are usually out of phase in this situation which seems directly proportional to the age of the aircraft. Thoughts and references appreciated.

[barit1]

Syncing N1 should make the most sense because it's the minor N1 residual imbalance that creates the heterodyne or "beat" frequency in the airframe.

However if N1 imbalance is so low that there's no perceptable beat, sync whatever parameter you like!

But it seems to me that other aircraft systems (hydraulics, inverters, ???) may create more cabin noise than anything else in cruise or especially approach.

[turrbntrip]

In the straight-wing Citations, one could select N1 or N2 ('Fan' or 'Turb').

Depended on who was aboard- As I recall, the crew could hear N2 over N1 at cruise, so we'd use that if we were empty.

With pax, they heard the fans in the back, so it was N1 sync if they were aboard.

TT