ATR Prop Brake ???
sik...@utrc.utc.com
I recently flew a short leg on an ATR aircraft. I noticed when the crew
started the right engine (couldn't see the left) the prop was held in
position by some kind of brake. The engine ran at gound idle for a
few minutes before the brake was released. When it was, the prop
spooled up real fast.
When we shut down, it was obvious the prop was stopped with some kind
of brake, while the engine continued to run.
My question... How many turboprop aircraft are equipped with a "prop
brake", and why?
James
Commutrdog
I fly the ATR and it is the only turboprop in production (as far as I
know) which has a prop brake. This device is used in lieu of an auxiliary
power unit, which is a small turbine engine used on many aircraft for air
conditioning and electrical power while on the ground.
The Pratt & Whitney engines on the ATR are of the "free turbine" type.
This means that the power turbine is not directly connected to the
propeller, therefore the propeller can be stopped and the engine can still
run.
The design of the ATR is such that for passenger boarding, either an
external power source must be available or an engine must be running. If
neither condition is met, there is no cabin ventilation and minimum cabin
lighting. There is much debate on the logic of this arrangement.
Aircraft such as the Jetstream cannot have a prop brake because the design
of their engines is different. There is a direct link between the engine
and propeller.
This was a very good question. You are quite observant.
Nick R.
NADIR
I personally know that the Saab 340, Atr42, Atr72 and some of the
Brasilias are equipped with prop brakes. The reason is it allows the
crew to run the engine to power the aircraft. Many of the smaller
airports do not have provisions for ground power for the turboprops.
More importantly, most airports lack cooling/heating units that can
fit a turboprop. One other thing, on quick turnarounds, waitng for
the electronic navigation equipment to spool up (which is usually done
after the engines are started) can add significantly to the turn
around time. Thus, to keep the passengers comfortable and the
batteries from dying, the crew engages the prop brake. This allows
the Air Cycle Machine to cool/heat the cabin and the use of electrical
power will not drain the batteries. Hope this clarifies things for ya
Loco Hombre
Marco Ghisalberti
> I recently flew a short leg on an ATR aircraft. I noticed when the crew
> My question... How many turboprop aircraft are equipped with a "prop
> brake", and why?
I don't know how many aircrafts are equipped with propeller brake but
the device is installed to use the right engine turbine as a source of
electricity and air conditioning for ground only use. When the right
prop is locked, the engine is running the "hotel mode" and the
throttles are not allowed to move out of ground idle. As a former ATR
pilot I really didn't like "hotel mode" due to the very low air
conditioning flow and the impossibility to use it during aft cargo
loading. ( right engine exausts directly to the aft cargo door ).
Another disadvantage is that during refuelling the right engine must
be stopped because the fuel intake is on the right wing, too close to
the engine running.
--
Marco Ghisalberti
Bergamo, Italy
Desrt Ratt
compressor bleed (used for air conditioning) and electrical loads without
having the expense and weight of an APU (auxiliary power unit).
Obviously the other benefit is eliminating risk of the rotating prop to
ground crew while the aircraft waits to depart the gate. Downside is
extra weight & additional failure modes for the engine, additional time &
cycles on the main engine, plus it's not as efficient as a dedicated APU.
I'm not sure what other turboprop A/C besides ATR's (with P&W 120-series
engines) have them.
sik...@utrc.utc.com
>James...
>
>I fly the ATR and it is the only turboprop in production (as far as I
>know) which has a prop brake.
snip
>The design of the ATR is such that for passenger boarding, either an
>external power source must be available or an engine must be running. If
I made another interesting observation during my (one-and-only) ATR flight.
While we were standing in line to board at the rear stairs, we observed
the nose gear lift off the ground about two feet! I was convinced the
tail-cone was going to hit the ramp. A quick thinking baggage handler
jumped up into the cargo area (fwd, near cockpit), and the nose
lowered.
I've heard stories about large jets falling on their tails, but it was
cool to see it happen. (Did you ever see the picture of the 727
popping a "wheelie" after a snow storm deposited heavy snow on the
tail??)
Are you ATR pilots familiar with this happening??
James
Mike Schwartz
American Eagle ( the largest US user) has opted to forego this
option citing costs.
One interesting note, the engines with prop brakes tend to be
larger fuel consumers due to heavy coking of the compressor
blades and turbine wheels.
NADIR
>snip<
> While we were standing in line to board at the rear stairs, we observed
> the nose gear lift off the ground about two feet! I was convinced the
> tail-cone was going to hit the ramp. A quick thinking baggage handler
> jumped up into the cargo area (fwd, near cockpit), and the nose
> lowered.
...
> Are you ATR pilots familiar with this happening??
Haven't seen that problem with the ATR's I worked on, but I did see a
picture of a cargo DC-10 sitting on its tail. The nose gear was at
least 15 feet in the air-would have loved to hear the loaders
explaining that!! Going back to the ATRs-the ones we operated were
loaded using the forward baggage area first, so it would be unlikely
that any of our aircraft did a tail stand. I do know some airlines
load the rear baggage area first, and this, combined with some other
factor may cause the nose to rise.
Commutrdog
I am not aware of any incidents where ATRs have done any tailstands. Our
airline flies the Shorts 360 and the Saab 340b as well as the ATR. The
ATR fleet is the only type which does not carry a "pogo stick" to put
under the tail to prevent such an occurance.
One scenario which could lead to the situation you describe would be (in
my opinion) if the airplane were empty, and the ground crew began loading
bags in the aft cargo area. If they were to fill the aft cargo to its max
capacity, and the forward area (cockpit and fwd cargo) was empty, a tail
heavy situation MIGHT be the result. Again, I have never seen this even
come close to happening, but I have wondered if it could be done.
Kevin M. Wilder
: Haven't seen that problem with the ATR's I worked on, but I did see a
: picture of a cargo DC-10 sitting on its tail. The nose gear was at
: least 15 feet in the air-would have loved to hear the loaders
: explaining that!!
"Tail sitting", as I have heard this problem called, is apperently quite
a serious concern. One airline (that will remain unnamed) that regularly
flies a 747-400 into YVR uses a "Pogo stick" while loading and
unloading. It is interesting to note that no other airlines that
operate this same aircraft type out of here use Pogo sticks. I wonder
if this airline has ever had a problem with their 747's tail sitting...
Regards,
Kevin
"The scientist explores what is; the
engineer creates what never has been."
- Theodore Von Karman
S. TOLBOOM
>a serious concern. One airline (that will remain unnamed) that regularly
>flies a 747-400 into YVR uses a "Pogo stick" while loading and
>unloading. It is interesting to note that no other airlines that
>operate this same aircraft type out of here use Pogo sticks. I wonder
>if this airline has ever had a problem with their 747's tail sitting...
Let me guess, it was a 747-400 Combi. If so it would be quite logical to use
such a stick, the reason the particular airline (KLM btw?) is the only one
who does this at YVR is that they are the only one operating combis into YVR.
Stephan
Len
>sik...@utrc.utc.com wrote:
>>snip<
>> While we were standing in line to board at the rear stairs, we observed
>> the nose gear lift off the ground about two feet! I was convinced the
>> tail-cone was going to hit the ramp. A quick thinking baggage handler
>> jumped up into the cargo area (fwd, near cockpit), and the nose
>> lowered.
>...
>> Are you ATR pilots familiar with this happening??
Last time I flew on an ATR (a 72) the flight crew took us off the
plane from the front back. 5 rows then 5 more rows then 5 more rows
until we got to the back. The reason they gave was that the ATR 72 is
tail heavy and might do a tail stand if there a bunch of passengers in
the back and baggage empty in front.
Len
---
sik...@utrc.utc.com
>plane from the front back. 5 rows then 5 more rows then 5 more rows
>until we got to the back. The reason they gave was that the ATR 72 is
>tail heavy and might do a tail stand if there a bunch of passengers in
>the back and baggage empty in front.
>
>
>Len
>---
Rethink your statement. Unloaded from the front first to avoid a tail-
heavy situation? Am I missing something?
Maybe that's why the pax door is in the rear. So the rear seats are
unloaded first. However, this still doesn't work becuase as the plane
empties, the folks that were in the front are all standing in the rear
(in line to exit).