Hi Bolkow,
Working for Heli-One, MRO provider for CHC and third party customers let me add the following.
A helicopter is just basically frame filled with a hand full of replaceable parts. So all the parts have their own limits and can be taken out of the “airframe time limits”
On some Militairy helicopters such an “airframe time limit” is known, for instance the Westland lynx has an airframe limit of 7000 hours. After that you need to throw away the aircraft. Currently some users have an extension till 8000 flight hours. Other operators have even reframed the helicopters when it reached 7000 flight hours, buying new frames and installing the old components. It could be that Westland put such a limit also on the Seaking airframes. These time limits are not so strange if you think that the Seaking and Lynx are helicopter originally designed to serve for 15 to 20 years and should have never reached these kind of flight hours.
Within the civil helicopter business (medium and heavy twin) I am not aware of 1 helicopter with an “airframe time limit”. We are known with heavy maintenance check, like G-Check and overhauls.
For an S61 it used to be at 10000 hours but has been increased up to 12500 (based on escalation of previous G-checks). After these hours you perform a huge airframe inspection (corrosion, cracks etc), rebuild the aircraft repaint if necessary and continue to fly.
The Super Puma has a similar inspection at 7000 flight hours or 10 years whatever comes first. In the reality is that Militairy organizations fly about 200hrs a year per aircraft, were commercial operators fly about 2000 flight hours per year.
This means that a commercial aircraft will see a G-check every 3 to 4 years based on the hour limit were the Militairy aircraft will see a G-check every 10 hours based on the calendar limit.
Cost wise these kind of G-checks will start around with a 7 figure number and will go up if the condition of the aircraft is poor. You can imagine that a Militairy aircraft flying over sea will have more corrosion issues during a G-check (after 10 years) then a commercial aircraft after 4 years.
From my own experience the S61 is one of the best airframes build ever, aircraft with more than 40000 flight hours are still in very good shape and easily pass the G-checks. So you are correct from a technical point of view there is no reason to ground the aircraft.
So basically it can be one of the following reasons:
1) Westland put a “airframe time limit on the frame” this cannot be ignored by the operator, so the need to ground the aircraft.
2) It is not financially attractive to perform a G-check, knowing the aircraft will go out of service within a view years.
However if they would like to have the G-check performed, we as Heli-One would very much like to offer our services!
Mark