Nine O Nine NTSB final report

[Pukeko]

7 hours ago, Pukeko said:

When I said "top of the red" ,that is  at and not exceeding 2800rpm.The rotor rpm was within the correct parameters for the corresponding engine rpm.I forget the "actual number" for the rotor rpm at 2800 engine ,as the last time I flew that particular type of aircraft was 1985.

New Englander, I found what I was looking for ;max  main rotor rpm =258 @104 %, min 170 @68 %.  These types of aircraft and other Sikorsky  models had a relatively slow rotor speed,and the slow speed would sometimes contribute to another "exciting " phenomena , "retreating blade stall" under certain conditions . That is a real attention getter,needless to say.The main problem letting rotor and engine rpm getting too low and pulling more  collective( main rotor pitch) it will further decay,contributing to over boosting due to the low engine rpm,and worse ,putting you into  a sometimes  non survivable situation.( rapid descent  vertically )The hulls on those machines contained a lot of magnesium ,and they can  go up like a christmas candle in only a few minutes !! Also you comment re dual tach totally correct,thanks .

[Dave Downs]

22 hours ago, New Englander said:

I think you're on the mark here. I really don't see why wide plug gaps would lead to detonation as much as an over boost would, especially since it's not known exactly when the detonation took place. One witness stated he heard a power increase just before impact and that's when an extreme over boost could have occurred - in the last desperate seconds in an attempt to save it.

For those not familiar, at that point the props should have been in max RPM, sort of like low gear. Advancing the throttles on a supercharged engine to to a very high manifold pressure even in "low gear" can cause extreme detonation. I've seen cylinder heads actually pushed off the barrels due to extreme over boost.

Just read the report - with my overwhelming 1500 hrs + of flight experience in piston-powered aircraft (about 1000 in the same 150hp Citabria) I was amazed at how badly things were handled. Just the statement that the flight engineer/loadmaster routinely did not occupy a belted-in seat violates one of my earliest instructions in aircraft operations. When I first started flying I would fasten my belt just to taxi the plane to the fuel pumps (and continued to do so throughout my flying years), and this was in a era when very few people wore seatbelts in their cars, in fact in 1965 few of us owned cars that had seatbelts!!

I do know a bit about the operation of high-performance gasoline piston engines (of the hot-rod type) and never heard of or experienced detonation due to overly wide spark plug gaps - detonation (and catastrophic engine failure) was often the outcome over over-boost!!!! Wide plug gaps usually resulted in missing/misfires at high rpms.

[m.c.farmerboy]

There are Old pilots and there are Bold pilots But Not Many OLD,BOLD PILOTS

[Dave Downs]

Another thought - @New Englander

The report mentions that the passengers were permitted to leave their seats and walk around while the aircraft was still in it's initial climb configuration. Doesn't that violate the FAR's? - not that it contributed to the accident but it seems like a very poor practice. I recall one of the early words of wisdom imparted by one of my flight instructors was that takeoff/climb was more dangerous than landing.

When I flew on the EAA B-17 many years ago there were no jump seats, all the passengers occupied a crew position (except for the tail gunner) and if my memory is correct we did not leave the seats until the aircraft was in a stabilized cruise configuration. I'm just surprised at how poorly the flights seem to have been operated - which unfortunately matches the poor maintenance.

[New Englander]

11 hours ago, Dave Downs said:

When I first started flying I would fasten my belt just to taxi the plane to the fuel pumps (and continued to do so throughout my flying years

Always a good idea, especially in a light plane. The guy in the jet or the air taxiing helicopter may not notice you or even have any idea of your vulnerability. I've seen bag carts, LD3 containers and even a van blown away. Company policy and regulation has always been belt on for taxi, even if repositioning to parking.

4 hours ago, Dave Downs said:

Doesn't that violate the FAR's?

The regulation states essentially taxi, TO, and landing, so an interpretation might include the below climb segments at most. Note that final segment, with no controlling obstacle ends at 1500'. I think that's as far as takeoff seat belt requirement could be stretched.