Jstflyin,
on all of the DH8-400s I know, there are all of the selections You mentioned available for the deicing boots. There is a 4 position switch that offers the following possibilities:
OFF: the boots are not running, but the governing valves are heated according to a schedule dependent on OAT (they are fed engine bleed air that of course contains atmospheric moisture and consequently might freeze up if they were not heated).
MANUAL: the boots are not running either, but the above mentioned valves are heated permanently. This position is used either when the automatic timer has failed or most often in case one single boot fails to inflate (indicated by the DEICE PRESSURE caution light) - virtually every time I have seen this, the selection of this position has freed up the associated valve and got the system going again.
SLOW: The boots are cycled upon initial selection with the following schedule: the boots are inflated 6 seconds each starting with each outboard wing section, then moving inward across 4 sections per wing (the inner two boots are out of line; the left inboard one is inflated simultaneously with the right 2nd boot and vice versa) and continuing with the tail (first inner elevator, upper rudder and #1 engine inlet, then outer elevator, lower rudder and #2 engine inlet). This is followed by a dwell time of 144 seconds - as the cycle takes 36 seconds to run, a SLOW cycle takes 180 seconds=3 minutes to complete.
FAST: Same as before, but with a dwell time of 24 seconds only. So one FAST cycle takes 1 minute only.
Additionally, there is an 8 position rotary switch (of which oddly 2 are OFF - seems there were no 7 position switches available to DH) that allows to activate the individual boot couples manually, should the timer fail (this is used together with the MANUAL mode on the mode selector). The PNF is required to move the switch to the next position every 6 seconds if needed, thereby effectively using up much of his capacity.
Luckystar,
As to when SLOW or FAST are to be used, does Your OM-B have anything to say about this? Here, SLOW is used on initial detection of ice; FAST is then used on pilots discretion when needed. The only execption is approach and departure - on approach in icing conditions, the boots are on FAST and on departure latest in 1000´ AAL they go on FAST as well. A holding in icing conditions also requires FAST to be selected.
By the way, those spigots on the wipers are not exactly reliable. Often have I seen quite a bit of ice accretion on the wing leading edges while the spigots and also the ice detectors were perfectly clean. Must have something to do with the different radii. A quick peek on the wing seems to be the most efficient way of looking for ice on the -400 just like on the older series.
Last edited by Tu.114; 12th March 2012 at 07:44.