Dhc8-400 Apu
 

Anybody would know the reason why can't we operate the Q400's APU in flight ??

Don't know
But the APU pack air intake is AFT of engine exhaust so you cant use APU BLEED after engines on

The APU in the DH8 100/200/300 is not contained in a fire-proof compartment, therefore its use airborne is prohibited. If the APU was left running, when the nose wheel leaves the ground, the APU will auto shutdown.

I've seen an occasion when so much freight had been loaded in a DH8-100 rear locker that the APU shutdown. Enter 10ish folk to the flight deck to depress the squat switch and restart the APU. Darn thing shut down again when they left! :cool:

I'd be surprised if the DH8-400 was significantly different.

very interesting comments............keep them coming
The instructor at flight safety said he'll answer the question later but he never did !!!

vickers vanguard
I'm sure Raj will get back to you when he can
'Now the thing is.......'

Sorry Just realised you are probably in Toronto and not Farnborough
So replace the word Raj with Sue

Is Raj still teaching the -400? :eek:

Yes Rich
But he works for FS now

Another fine example of Flybe not quite retaining key staff.

Great guy & technically excellent.

We miss you down here Raj

Regards

BAe146??? And poor Management???:{:{:{

guys guys ..........and girls, let's stay with the subject ! we don't want another Flybe bash in here. It's Flight safety Canada in Downsview/Toronto........and as far as instructors go, there have been 4 different ones over a 2 weeks period, it looks like everybody is part time down there, what give??????

The same limitation applies to the 100-200 series, the ESU will auto-shut the APU(pseu signal) if you take off with the APU running. I don't believe it has something to do with the engine exhaust since the AFM says for ground use only and does specify if the engines are running or not.
Another member mentioned the Apu compartment being not fire resistant. VEry possible explanation, any reference for that ?????

Don't know if this helps, but I've heard that Bombardier is working on a mod that will allow operation of the APU in flight ( for the 300 series, not certain about the 400)

Hi,

the -400 APU is simply not approuved for the -400.If it bursts noone knows what will happen.To get to know this you have to to testing and this costs.
Anyway the elektrical design is from -100 wich had no APU original.The disadvantage to bring it into safty design is to have another AOG Risk Item wich is now Cat D (120 Days) .APU could easyly bring it into TOP 5 AOG drivers.


Sparkies

Not much insight offered, but the Dash APU is simply not certified for inflight use. I don't know what extra hoops are required for that but DHC probably felt there was no need to certify it as it's not really required for any redundancy.

On the Fokker 70/100 and CRJ the APU generator is used to provide redundancy in case of failure of an engine driven generator. The Dash 8 has four engine-driven generators anyway, two of which are sufficient to power all electrical systems (sans Galley on the -400 if I recall correctly).

Bleed Air (which is AFAIK provided by the APU on the CRJ for anti-ice on approaches) is not an issue on the props with their deicing boots. So why should DHC bother to do extra certification work on a system that is considered a subsitute for GPU and ground Airco and that is often U/S even when used on the ground only (on the -400 the APU generator seems to be too weak for even normal ground use).

The APU design is BTW completely different on the -100/300 and -400. The -400 has the APU in the very end of the tailcone while the older Dashes have it in the rear fuselage.

And, the DH8-100 certainly came with an APU unless the customer requested no APU.

Actually, the APU is on the MMEL as a category C item (10 days), and is not taken credit for in safety analyses, for the same reason as mentioned above (too much impact on dispatch reliability)

On the Dash 8 it is MEL Cat. D, i.e. 120 days (or hot all of summer, cold all of winter...)

I didn't want to imply that dispatch without APU is impossible on the CRJ/Fokker, it's just more of a nuisance because you need a jet starter for every turnaround. I'd imagine you'd have some restrictions on minimum thrust if you fly the CRJ in icing conditions without APU. (Fokker doesn't use APU bleed while airborne.)

Trust me,the Q400 APU is so dreadfully unreliable in my experience you wouldn't want to be reliant on it in flight. I would have to recommend that Bombardier get its basic on-ground operation sorted before they throw money at making it 'useable' in flight. It is an almost daily source of irritation and frustration.

Given that the DH8 design is some 20 years old, I suspect that recertification to allow airborne APU use is not too high on Bombardier's list of priorities.

Capt Claret gets the banana for answering the original Q ...

Answer: Because de Havilland did not design and certify the installation for airborne operation.

ps. The Q400 APU is reliable enough once it is running - it's the start sequence that kn***ers it. And don't spray de-icing fluid into the intake.