View Full Version : Dash8-400 question

24th Aug 2011, 10:53
Hi all, i posted this same thread on spectators balcony forum first, and they recommended i post it here.

I am writing a paper on Dash8 avionics and instrumentation. I have been good so far, but have problems with inspiration on two chapters i need to write:
1) Functional and ergonomic limitations of installing components
2) Suggestions for possible improvement of avionics and instrumentation

Now for the second chapter in question i suppose i could take a newer avionic system from a different plane, and then analyze and compare it to dash8 avionics?
But on the first one i am completely lost.

If anyone is flying on the Dash, i would appreciate if they would comment on the avionics, and what they think could be improved.

Please help me on this, any help is appreciatedhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif

Artificial Horizon
24th Aug 2011, 11:44
From an automation point of you the ATL SEL feature is a bloody nightmare, why allow someone to select an altitude that WON'T capture!!

Secondly, the two independent HDG selectors!!! WHY!!

24th Aug 2011, 12:24
A lot could be improved. The avionics, and in fact the whole plane, has heaps of potential but has been artificially dumbed down to keep it operable under common type rating with the older series.

That vile altitude select system has been mentioned, as has the heading bug system, and I fully agree to what Artificial Horizon has said.

In addition - the speed bugs. There are two to five of them on screen (depending on situation), but only those for V1, Vr and V2 can be set from one point to be displayed on both sides. The remaining two bugs (their use is SOP dependent of course, but in my company they are used for minimum speeds and approach speeds) have to be set individually by each pilot. Now in case the autopilot is u/s or the PF is flying manually for any other reason, he will need to reach down to the control panel and reset the bugs whenever any flap setting is altered himself instead of having the PNF set the bugs as it should be. And on top of this, this is done by a much-loved single button with a million functions. You cycle through the different bugs using one button and then twist another knob to set the value.
Another little favourite of mine: when setting V1, Vr and V2, You set V1, then cycle to Vr and have to begin at 0 again. Is there ANY situation when Vr is lower than V1 or V2 lower than Vr? Why cannot Vr be initially equal to V1 and V2 equal to Vr - that would save much time inserting those speeds.

Staying with the ASI for a moment. That ADC can compute all those fluctuations of Vne and duly indicate it, but it can NOT set the Vne bar to the actual maximum speed when flaps or gear have been extended. So whatever the configuration, the indicated Vne is always at 246kIAS below 8000ft, while for example the actual Vmax is 200kIAS with Flaps 5 and 182kIAS with flaps 10 (both typical T/O settings). Now let ATC call You to level off early after T/O or better in a G/A with its systematically high workload in this A/C and remember that this aircraft is quite well powered - a flap overspeed in that situation happens much more often than it needs to, and just 5 or 6 simple lines in the code (such as IF FLAPS=5 THEN VMAXindicated=200) would provide a VERY obvious cue.

Now to the descent. A "banana" (indicating on the ND the point along the route where with the current G/S and V/S the armed altitude will be reached) would be a very valuable tool and again require only a line or two in the programming code, but obviously it is not needed.

Also the tradition of placing much-used levers in weird places has been well honoured in the -400. From the -300, I fondly remember the synchrophase switch that had to be operated by the PNF after departure and before landing - and of all the places to put it, some wise guy elected to stick it on the glareshield in front of the R/P. And on the -400, it is the flight/taxi switch that needs to be switched during lineup and after runway vacation by the RP but has been set in front of the L/P on the glareshield.

One might also look at the gear lever here - it is placed on the R/H center panel well in reach of the copilot, but not so from the captains side.
The already mentioned instrument control panel comes to mind as well - it is situated outside of the PFDs on the instrument panel and one has to bend well forward to reach it for any adjustment, be it to the speed bugs, the minima or the altimeter reference pressure.

All in all, the ideal DH8 pilot has the body features of a gibbon - short, stubby body (but not too rotund, lest he does not fit through the escape hatch!), shortish legs, but extremely long arms to reach all those weirdly located levers.

One little other thing comes to mind - the course selector on the glareshield. During the approach preparation, the course arrow will be briefly selected for display, then adjusted and then it will be deselected for the Nav display to come up again. Only when leaving FMS navigation for the final approach, the course arrow will be displayed again, this time in the HSI on the PFD. But keeping in mind the general system philosophy hinted at before - will the course selector be locked out, when the arrow is not displayed? Of course not - so if one inadvertently twists the course selector after having dialed the approach course, one might end up with a little surprise when resuming conventional navigation. Again, it would have taken one single line in the code to allow course selection only when the arrow is displayed somewhere.

I am sure I will come up with one or another thing later on when thinking about it a bit...

24th Aug 2011, 14:06
Thank you very much, this will be very useful. I also hope that some Dash8 engineers are reading this too, and maybe take a note or two;)

29th Aug 2011, 13:21
If anyone has anything to add, like are the screens visible enough, or are sounds audible enough, anything that you might think could be improved, as i unfortunately have no access to an actual cockpit, please do say.


30th Aug 2011, 17:24
I'm not a Dash 8 -400 pilot but I do have a lot of time on the -300 series.

I believe many of the shortcomings of the -400 series were deliberately "built in" to maintain the common type rating with the -100/200/300 series. Some of these "problems" can be switched off by operators who only operate the Q400. These include such as the independent heading bugs, the need to arm ALTSEL and the way airspeed and V/S is presented on the PFD (Instead of the tape style display operators can chose a round dial presentation identical to the -300 series).

Maybe you could compare the Q400 avionics with the SAAB2000? Both aircraft were faster, more advanced stretches of an earlier model, but one manufacturer chose to maintain commonality with the parent aircraft while the other did not.

30th Aug 2011, 19:13
Tu.114 has elegantly put across the key issues with the Q4 avionics. Personally I would have just used a 4 letter word. The ALT SEL system is unwise.

31st Aug 2011, 12:34
Again, thanks for the replies.

I am confused about the ALT SEL function though.

A copy/paste from AOM:

This automatically arms the Altitude Select mode. When the aircraft baro corrected altitude
approaches the Selected Altitude target, the FD automatically transitions to the Altitude Cap-
ture mode and begins to return the aircraft to level flight. When the Selected Altitude target has
been captured, the FD automatically transitions to the Altitude Hold mode and maintains the
Selected Altitude.

So when a pilot selects the target altitude, he has to switch to another mode or maneuver the aircraft himself to that altitude? What's the point of ALT SEL mode then?
Am i missing the point here?

31st Aug 2011, 13:30
As ATP-Al among others has mentioned, there are many little things of nastiness in the -400 that have been deliberately installed due to type rating commonality between all the DH8 series. I would not be surprised if the Alt Sel was one of those items - the DH8A was designed in the late 1970s and it might well be that automation at that time required such weird (from todays point of view) solutions. Someone knowing those planes will surely be able to confirm or correct me, but I seem to remember having read about a similar system in early 747 models.

I do not know the Dash 7 either - one might think that DHC took that Alt Sel system over from this type to maintain a bit of fleet commonality. If anyone knows that type, I would be very interested to hear about this.

Operationally, this system seems to be pretty useless. The only situation I can imagine where one would not want to capture a selected altitude upon reaching it would be on approach when e. g. capturing the ILS glide slope from 5000ft with a missed approach altitude of lets say 3000ft required and dialed in on that occasion. Now while tracking the GS, an altitude capture at 3000ft will obviously be most unwanted - but Alt Sel on the -400 is inhibited when in G/S tracking mode...

Another thing just crosses my mind looking at approaches. The Localizer capturing mode is not at all perfect - it will work fine in calm wind, intercept angles of around 20 and airspeeds of not more than 180kIAS. Anything other than that - be it fairly typical speeds of around 200 or 220 knots on intercept, a moderate crosswind or an innovative intercept heading - will result in the autopilot and flight director oscillating about the localizer several times with the amplitude decreasing on each curve. In such a situation, briefly disregarding the flight director and manually setting the aircraft on the track is a proven solution.

In fact, the -400 capture logic appears well suited to -300 speeds while this type suffered from the same problems, albeit at its typically lower speeds.

Another little thing I personally dislike a bit is the aircrafts reliance on several buttons to cycle through indication modes. Be it EGPWS display vs. WX radar, TCAS AUTO vs ABV/BEL (resulting in a popup mode I will discuss later) vs. permanent display or the display of navaids and/or airfields on the ND, it all is selected via such buttons. After powering up the A/C, all those displays will default to a dedicated setting; they will do the same occasionally after generator switching common at startup or shutdown. So it is not possible to keep the displays locked to a certain setup for the duration of the duty like it would be possible, had DH installed 3-way rotary switches for example or push buttons that mechanically lock on or off. Instead, one will need to periodically build up the desired displays, usually every time after the props have unfeathered after startup.

Now to that TCAS. While it basically works like in every other plane I know, it has two little particularities on the -400. Firstly, it does not automatically display traffic in the selected altitude range - on power up, it is in the praiseworthy AUTO mode and will do its work mostly shrouded in secrecy. It only displays RA or TA traffic (which will then pop up on screen together with its dedicated aural alert), on occasion causing some surprise when one has never had the opportunity to view the intruder close in when he still was a blue square. Also, any other mode than AUTO is only displayable at ND ranges of 40NM and below - while I realize that greater ranges tend to clutter other traffic around the A/C symbol a bit, I would still find it nice to at least see that there is something around in order to select an appropriate smaller range when required...

I realize that my personal preference plays some role in what I just wrote - anyway, with some minor changes, the ergonomics of that plane would be agreeable and the workload much reduced.

2nd Sep 2011, 23:24
So how does it compare with the ATR 72 (500/600 Series)?

5th Sep 2011, 15:13
I am also interested to hear how the avionics compare to ATR-72, especially the -600, with it's full glass cockpit that i am currently trying to find AOM for, or any manual, so i can analyze it.

I suppose, because of the full glass cockpit, q400's avionics, despite it's quirks, is much more user friendly/ load reducing than the atr-72-500.

Although there is a whole bunch of threads about this very comparison on pprune (and i am looking through all of them), any additional first hand experiences from you guys would be great to hear!

5th Sep 2011, 22:31
A bleed air system which works by providing airflow and not only pressure would be nice, too.
The Q400 can produce over 100 psi of bleed pressure creating lots of noise from the gaspers but ventilation is still poor.
And speaking about air conditioning the dependent bleed ducts which can't be more than like 10 kelvin apart from each other are just silly.
A full load of passengers require cooling even on a cooler day but the guys upfront will be freezing as they can't select the duct temp high enough without baking their passengers...

7th Sep 2011, 09:38

The alt capture system on most aircraft works as follows: set desired altitude/flight level, point aircraft towards that altitude, let the system capture it. It will leave that altitude only if you deselect it or you capture the glide slope of an ils (having first captured the localiser).

Not so the mighty dash 400.

Firstly select desired altitude. then press the alt sel button, cross check to ensure that alt sel is displayed on the screens. point aircraft towards selected altitude. Monitor like a hawk to ensure that the alt sel does not drop out. Within one to go (1000' of desired altitude) touch nothing or you will inadvertenly deselect alt sel, monitor even more closely with hands on the controls poised for the system to fail to capture. System captures desired altitude, breath sigh of relief that you haven't had an alt bust. repeat for all level changes during working day.

(The system works for glideslope capture as above, and you can leave alt capture by engeging any vertical mode ( ie IAS, VS Pitch hold).

The problem is that without the alt sel selected the aircraft will fly through the selected altitude, the alt sel system is very prone to drop out and this can be missed in a busy environment. It is a fail unsafe system.

The autopilot can aparently also revert to basic modes from aparently stable conditions such as alt capture and glide capture all by itself.

The alt sel feature is not an option on the instrument fits unlike coupled heading bugs etc and aparently is a major software and expensive fix.