Dash 8 Emergency Window Exits

[LimaFoxTango]

Hi all. My company has started to re-activate the Ditching Dam system on our 300's which now enable us to operate at the higher TOW of 43000lbs as opposed to 41100lbs. My questions is, is the theory of the emergency window exits allowing water to enter the cabin in a water landing (at the higher weight) the real story behind the DD? How did Bombardier (or maybe deHavilland at the time) figure this out?

Secondly, I realize the Q400 does not have emergency window exits and thus no DD system. Since the fuselage is obviously the same as the 100/200/300 the higher weight of 64500lbs must be a reason for its removal, or is it something else?

I'm always amazed of aircraft manufacturers design the location of emergency window exits. In the 100/200's they're located ahead of the wing versus the 300's which is located aft of it.

[Otto Throttle]

LFT

The Q400 does have a ditching dam system, although on this version the dams are fitted to the forward pax door and the forward right emergency exit. As the 400 has a rear pax door and a rear service door, there is no need for additional emergency exits located near the wing (at least according to the certifying authorities.

The theory behind this arrangement is that in a water landing, the two rear exits are expected to be unusable, but with the DD in place, the two forward exits should be serviceable. I don't think this has anything to do with a higher gross weight, but more the length of the airframe and the 'normal' weight distribution.

[Alpine Flyer]

The Dash 8-100 emergency exits are probably located in a rather forward location to keep them available when the (optional) moveable rear cabin bulkhead is moved to the most forward position, leaving only 5 rows of seats. The exit would then be in the second row from the rear, the rearmost probably being impractical because of e.g. the exit overlapping with the bulkhead.

AFAIR a Dash 8(-300?) crash landed during a bungled swingover in CDG in the early 90s and the wing spar came down and blocked access from the forward to the rear cabin. In a -100 that would have left you trapped in the rear cabin.

I don't think either the -300's or the -400's ditching dams have ever seen more water than a cup in the cabin or rain outside. The -400s dam for the airstair door is a rather flimsy piece that slides down from abvove the door and doesn't look very watertight. The right forward emergency exit is a two-piece affair where the lower part is blocked for ditching. The -300s inflatable dams sometimes go off in flight....