Bae-146 Questions...

[DVR6K]

Hi all,

Was watching a DVD on the Bae-146 (one of those flightdeck ones) which has raised a few questions I have been unable as yet to find answers to on PpruNe...

I was wondering where I might be able to find info about the TMS. Where does it get the variables from to calculate flex N1 settings etc as I didn't spot any kind of CDU in the flight deck a la Airbus for example? Also, the crew at one point used TGT as a measurement to maintain cruise thrust. How is TGT more favourable to use than N1 or EPR?? Surely TGT will vary with ambient conditions.

Also was wondering about the speedbrake selection. I understand it is an effective beast as it is used on the STOL operations. However, on the way into Ciampino, these guys had the thing fully deployed and then selected lift dumpers on the ground. Have seen many pictures of the 146 with the speedbrakes open whilst hurtling down the glideslope on approach to a long runway, so why deploy them?

Does anyone know where I might be able to get hold of a manual for the 146? Would be interested to learn some more about this a/c, plus add some strings to the bow for those airline interviews!!

Thanks.

[CarltonBrowne the FO]

Using TGT in the cruise to control thrust allows you to gain maximum thrust, as you can run all four engines at max continuous thrust.
TMS could be used to control engine thrust in three main ways: matching TGTs, matching N1s and matching N2s. Most of the time we would match N1; with all four fans running at the same speed, cabin noise was reduced. Theoretically, at higher levels N2 matching would be better for achieving low cabin noise- however, in practice N1 was almost always used instead.
My preferred TMS mode in the cruise was a combination mode, where one selected the TGT on the "master" engine, and the other 3 then matched their N1s to it. This kept the cabin noise to a minimum, but allowed thrust changes to be done using the thumbwheel of the TMS TGT controller.
Airbrakes could be used on the ILS in 2 ways. If asked by ATC, the aircraft could be kept at very high speeds till late on the approach (my personal best was 190 knots to 3 miles) then the airbrakes used to decelerate very rapidly indeed, and still achieve a stabilised approach by 500 feet. On a normal approach, however, airbrakes would be opened after decision altitude (usually between the airfield boundary and the threshold) to reduce speed from Vapp (usually Vref +5) to touchdown speed (usually Vref-7 or so).
Unfortunately I can't remember how we set the TMS for departure- it's been a long time, and I don't have my 146 manuals to hand...

[xodus]

TMS is set to T/O (take OFF) for departure. provides the thrust calculated by the TMS computer. By tricking the computer into believing it is hotter than ambient you can achieve flex.

But with four hairdryers under your wings, the 146 at full flex can chew a considerable amount of road.


As for the manuals, If you buy a 146 Im sure they will come included :}

[safetypee]

On the ground the BAe146 TMS default temperature was the sensed ambient from the TAT probe. However, the tower temperature should always be set as the TAT probe could suffer errors due to reflections from hot concrete, etc. If you didn’t have a tower temp available in foreign parts / hot climes, then use a wet face cloth to cool the probe down!
A flex takeoff used the assumed temperature method; a false ambient temperature is set in the TMS. The flex N1 must be checked against the tables of expected and allowed thrust reductions.
The TGT mode with N1 synchronisation to the hottest engine was used during the climb to maximise engine life; the cruise was normally flown in N1 sync. The engine does not use EPR. The Avro RJ has a different system embedded in the flight guidance computer.

The airbrake was very effective; a selection on late finals gave a consistent speed reduction for the flare and landing. The airbrake and full flap were mandatory for steep approaches as they provided a larger drag margin to manoeuvre the aircraft about the glideslope.

[banana head]

The airbrake is deployed late on the approach only to facilitate the selection of lift spoilers on touchdown ( as both systems are combined on the same lever).
The fact that the airspeed naturally bleeds from Vref33+5, or whatever your selected increment is to Vref33 ( or if you place faith in BAe's Training guide Vref33-7kts) for touchdown is coincidental.

Use of the airbrake to stabilize the aircraft when conducting a steep approach is an entirely different matter - it is simply necessary in order to maintain a stable speed while having a suitable approach power setting (as per certification requirements). This is the principle reason many other small regional jets are unable to be certified for steep approach op's such as LCY. (i.e. they don't have a tail brake/ airbrake and cannot produce sufficient drag with flap alone).

Carlton Browne, you say "Using TGT in the cruise to control thrust allows you to gain maximum thrust, as you can run all four engines at max continuous thrust.
Sorry mate, but then why have an MCT mode?? and as underpowered as the 146 is, I have never needed to use MCT in the cruise, even with an engine out.
I personally used to use TGT SYNC in the cruise only because I am incredibly lazy and wanted to be able to make small trust changes by playing with the TGT thumbwheel rather than actually having to move the Trust levers. I would suggest that this is probably what you observed on your DVD safetypee

[CarltonBrowne the FO]

I haven't flown a 146 in five years, so my memory is undoubtedly faulty... the company I worked for had a quite mature fleet; the engines had suffered some abuse in their lives, and sometimes climbing, and then accelerating, over the Alps in summer was a protracted process. I think we were told not to exceed 800 degrees TGT in the cruise- I don't remember there being an MCT mode in the system, but I could be wrong about that.
Perhaps the 800 degree limit was a lower temperature than the absolute Max Continuous, intended to extend engine life?
Like banana head, sheer laziness made me use the TGT thumbwheel to change thrust settings in the cruise; my preferred mode, however, was only to control the master engine in this way- I don't remember the name of the mode, but it is definitely possible to control one engine's TGT, while slaving the other 3 to match its N1. Where possible, I would choose the hottest engine as master- that made it easy to ensure none of the engine TGTs exceeded 800 degrees.

[Capt Claret]

Joe

I haven't noticed any performance change with the roll back mod, and the whole fleet's been done, except that the FL260 flight planning limitation has been removed, as has the limit of FL260 in icing conditions!

I'm curious as to what semblance of power loss you've noticed.