Flaps and Reverse on DHC-6
JammedStab
The old 100 and 200 series aircraft that did not have Mod 6-1223 had the flap switches that were interconnected to the "Reset Props Lights". Without the flaps down the light would be on even if the other electrical conditions were met - but there was no preventative system installed to physically prevent the movement of the power lever into reverse. Just the "Reset Props Light. The switch was rigged to actuate at 7 1/2 deg. flap down. With the Mod the switches could be removed which left just the propeller control switches operating the lights.
Most aircraft have this system removed and actually the only place that I remember it being described is in TAB (Technical Advisory Bulletin) 610/2.
Quote - DHC TAB 610/2 - Section 31 - Page 1
""Mandatory Mod 6-1223 provides an interlock witch makes impossible the selection of reverse with propeller levers set below 95% . With Mod 6-1223 incorporated, functioning Reset Props light cautions the pilot that "Reversing" will be impossible, unless propeller levers are advanced to Max RPM setting.""
Old airplanes often have lots of history - and some of us helped make that history. About 1975 or 76 I was right seat in the -6 on a Medevac run in the dark of night at about -30 Deg F. On the takeoff run with the nurse and patient on board we had an uncommanded right engine auto-feather right at liftoff. Severe "Black Hole" effect and there was some pretty fancy hand and foot work in the cockpit. We clipped the trees with the landing gear on the way out - straightened everything out and flew back to base. We were just one of a few that this had happened to - DHC solution was an upgraded autofeather system relay - so no one else has this issue.
The constant progression of aircraft reliability is often a very direct function of feedback from incidents like this.
There are reasons for the operation of the aircraft with adherence to the Flight Manual - Reducing noise or a short field landing that is not within the normal operation limits published for the aircraft are not acceptable reasons to deviate from the approved procedures. If the checklist calls for "Props Max RPM" on the approach then that is where they should be. Operating the aircraft outside of the requirements will bite your a$$ at some point. You might think this system is a hazard - and you should voice your opinion about it - but do it to someone who can do something about it - the manufacturer!!!
Write them with all the details of what you have for concerns - and expect that they will stand behind their published procedures - those procedures cost them a lot of money and were done by men better able to access the dangers than I.
Don't know about you because for all I know "You are a certified "Test Pilot".
(No I am not being sarcastic - I really don't know what your qualifications are.)
Hope this helps a bit.