On the inside of the starboard engine of the Bombardier Dash 8 Q400 there is a small aerofoil shaped object* protruding from the casing. There also appears to be pipes protruding from the end of it.

Can anyone identify what this is and explain its function?

Own photograph

** Probably not an aerofoil just looks vaguely like one.


2 Answers 2


It is the engine drain mast. From the Dash 8 Series 400 airport planning document - Chapter 2, Page 40:

Dash 8

Dash 8 engine drain; image from Dash 8 Series 400 airport planning document

Basically, the drain mast houses the drains that allow for the removal of the fluids (oil and fuel) that come out of the engine, due to seepage, leaks etc. For example, this incident report is a case where it was,

... observed ... fuel dripping from RH engine drain mast.

  • 5
    $\begingroup$ And what does it do? Can you explain it's function? $\endgroup$
    – J W
    Commented Apr 25, 2017 at 13:31
  • $\begingroup$ @JonathanWalters it drains the engine, obviously! :) Of what, I haven't a clue... $\endgroup$
    – FreeMan
    Commented Apr 25, 2017 at 13:43
  • 8
    $\begingroup$ @JonathanWalters Oil can get "hidden" in various places inside a running engine, but after shut-down finds its way to the lowest point, which may not be back into the oil tank. Fuel systems can also develop minor leaks, like any other plumbing system. The drain system is there to get the unwanted fluids out of the way before the engine is restarted - you don't want pools of flammable liquid sitting around where they shouldn't be. Anti-icing operations on the ground, washing the fan blades for inspection after foreign object ingestion, etc, may also cause fluid to get into engines by accident. $\endgroup$
    – alephzero
    Commented Apr 25, 2017 at 15:16

It's a drain, as explained previously... PW100 series tend to leak a lot of oil as part of their design, so this is a drain where leaks from normal, healthy, places can come out. The design of the drain keeps the oil away from the nacelle so it's easier to differentiate normal oil seepage from an abnormal leak... which would spread orange oil all over the nacelle cowling. (A bit of oil coating everything is not that abnormal, a lot could be cause for concern, or at least checking the oil level of the engine)

  • 1
    $\begingroup$ Welcome to Aviation.se! $\endgroup$
    – Ralph J
    Commented Apr 26, 2017 at 3:12

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