747 engine takeoff power

I have a question for anyone familiar with flying the 747-200.

According to news stories in the media reporting the crash of a
MK Airlines 747-200 freighter at Halifax Canada awhile ago, the
investigators found that the airspeed was some 55 kph low. It was
noted that the engines had been operated at a power 'inconsistent
with the a/c weight' (as if the engines are normally operated at
a power governed by the a/c weight during takeoff).

Is this true for this a/c?

I've never heard of this. Any a/c that I'm familiar with
certainly don't modulate takeoff power according to their weight.

Is it done on the 747?
--

-Gord.
(use gordon in email)

I have a question for anyone familiar with flying the 747-200.
BRBR

The 747 with or without the tailhook??

Sorry, just a little holiday humor. Ohh so many guys here that are flying the
big winged buses, wondering about their future.
P. C. Chisholm
CDR, USN(ret.)
Old Phart Phormer Phantom, Turkey, Viper, Scooter and Combat Buckeye Phlyer

Gord Beaman wrote

I've never heard of this. Any a/c that I'm familiar with
certainly don't modulate takeoff power according to their weight.

It can be done for most all jet transport category aircraft.
It is called the "reduced takeoff thrust" procedure. Most
airlines have FAA approval to use this procedure in order
to extend engine life. It's all about "creep units", RPM,
and EGT or TIT. Keep the RMP and EGT as low as possible for
extended engine life.
It goes something like this......
From the runway takeoff limit chart, determine the maximum
allowable temperature for the actual weight. Then use that
assumed temperature to determine the takeoff power setting.
This will produce takeoff performance equal to a takeoff at
maximum weight for the actual temperature.
I'll scan the procedure out of my Boeing manual if this is
not clear enough.

Bob Moore
VP-21 VP-46
ATP B-707 B-727
PanAm (retired)

Bob Moore wrote:

Gord Beaman wrote

I've never heard of this. Any a/c that I'm familiar with
certainly don't modulate takeoff power according to their weight.

It can be done for most all jet transport category aircraft.
It is called the "reduced takeoff thrust" procedure. Most
airlines have FAA approval to use this procedure in order
to extend engine life. It's all about "creep units", RPM,
and EGT or TIT. Keep the RMP and EGT as low as possible for
extended engine life.
It goes something like this......
From the runway takeoff limit chart, determine the maximum
allowable temperature for the actual weight. Then use that
assumed temperature to determine the takeoff power setting.
This will produce takeoff performance equal to a takeoff at
maximum weight for the actual temperature.
I'll scan the procedure out of my Boeing manual if this is
not clear enough.

Bob Moore
VP-21 VP-46
ATP B-707 B-727
PanAm (retired)

Thanks Bob, and that's quite clear, no need to scan it at all. I
just had never heard of it being done before. Seems like a
somewhat unsafe thing to be doing with a high value machine in a
highly critical phase of its flight.

Perhaps 'unsafe' isn't the correct word here, my point is that I
feel that it might be unproductive to operate the a/c closer to
it's maximum capabilities just to save some 'wear and tear' on
the engines? I'd think that you're not availing yourself of that
'extra performance' in case of an engine failure at a critical
time. I suspect that it'd take a hell of a long time to make up
what they lost in that one crash. (not even to mention the seven
crew-members)
--

-Gord.
(use gordon in email)

"Gord Beaman" wrote...

Thanks Bob, and that's quite clear, no need to scan it at all. I
just had never heard of it being done before. Seems like a
somewhat unsafe thing to be doing with a high value machine in a
highly critical phase of its flight.

Perhaps 'unsafe' isn't the correct word here, my point is that I
feel that it might be unproductive to operate the a/c closer to
it's maximum capabilities just to save some 'wear and tear' on
the engines? I'd think that you're not availing yourself of that
'extra performance' in case of an engine failure at a critical
time. I suspect that it'd take a hell of a long time to make up
what they lost in that one crash. (not even to mention the seven
crew-members)

Well, this is just an example of the reality that belies the "safety is
paramount" theory... Reduced T/O thrust and non-optimum noise abatement climb
profiles have been made "standard" to put economics and politics ahead of actual
safety considerations...

There are actually some limited cases (e.g., contaminated runways, to reduce
Vmc) where reduced thrust takeoffs are "safer" than full-thrust takeoffs, but
they are the exception to the rule.

"John R Weiss" wrote:

"Gord Beaman" wrote...

Thanks Bob, and that's quite clear, no need to scan it at all. I
just had never heard of it being done before. Seems like a
somewhat unsafe thing to be doing with a high value machine in a
highly critical phase of its flight.

Perhaps 'unsafe' isn't the correct word here, my point is that I
feel that it might be unproductive to operate the a/c closer to
it's maximum capabilities just to save some 'wear and tear' on
the engines? I'd think that you're not availing yourself of that
'extra performance' in case of an engine failure at a critical
time. I suspect that it'd take a hell of a long time to make up
what they lost in that one crash. (not even to mention the seven
crew-members)

Well, this is just an example of the reality that belies the "safety is
paramount" theory...

Yep, I agree...and further, I think they're right to do so too.
I've said this before (and gotten slapped down for it) I think
a/c are too safe now...we need to allow the safety factor to
slowly float downward until it's close to the 'safety factor plus
the financial risk factor of the automobile'. At that point the
passenger will still be much safer in an a/c than an automobile
because of the much higher financial risk factor of the aircraft.
BUT the cost for an airline ticket won't be so prohibitive that
lots of people will drive rather than fly. Or are the airlines
fully utilizing the available airspace in North America therefore
there's no opportunity to increase air traffic?


Reduced T/O thrust and non-optimum noise abatement climb
profiles have been made "standard" to put economics and politics ahead of actual
safety considerations...

There are actually some limited cases (e.g., contaminated runways, to reduce
Vmc) where reduced thrust takeoffs are "safer" than full-thrust takeoffs, but
they are the exception to the rule.


John, I recall that you're a qualified 747 F/E or Pilot so can
you tell me whether replacing aerodynamic trim of the tailplane
with fuel weight to reduce drag during cruise is still being
done?...I never seem to hear of it anymore, also what's the
proper nomenclature for that?
--

-Gord.
(use gordon in email)

Gord Beaman wrote

John, I recall that you're a qualified 747 F/E or Pilot so can
you tell me whether replacing aerodynamic trim of the tailplane
with fuel weight to reduce drag during cruise is still being
done?...I never seem to hear of it anymore, also what's the
proper nomenclature for that?

We never did the fuel thing in the B-707, but we did try
to keep as much luggage/cargo in the aft hold as possible
in order to accomplish the same thing.

Bob

"Gord Beaman" wrote...

John, I recall that you're a qualified 747 F/E or Pilot so can
you tell me whether replacing aerodynamic trim of the tailplane
with fuel weight to reduce drag during cruise is still being
done?...I never seem to hear of it anymore, also what's the
proper nomenclature for that?

I'm a 747-400 Pilot.

Some 744s were delivered with fuel tanks in the horizontal tail. They hold
10,000 Kg. I have not flown any airplanes with them installed, so I do not know
any fuel management specifics for them.

While it may be possible to "passively" manage the CG by retaining the tail fuel
as long as possible, I don't know if this is authorized. Also, AFAIK, there is
no way to move fuel to the tail tank in flight -- once transferred down, it
stays down.

Gord Beaman wrote

Perhaps 'unsafe' isn't the correct word here, my point is that I
feel that it might be unproductive to operate the a/c closer to
it's maximum capabilities just to save some 'wear and tear' on
the engines? I'd think that you're not availing yourself of that
'extra performance' in case of an engine failure at a critical
time.

Gord, I post the following excerpt from the excellent book,
"Handling the Big Jets" by D.P. Davies, the Brit who certified
the B-707 in Britian as Chief Test Pilot for the United Kingdom
Airworthiness Authority.

---------------------------------------------------------
The overall safety level of reduced thrust take-offs is
something which bothers some pilots, who believe that the
average exposure to `near critical' take-off conditions
is increased. The proof that this worry is groundless is,
as one would expect of something produced by performance
experts, long and detailed. However, the following is a
brief outline:
When reduced thrust is used for take-off the risk per
flight is decreased because :
(a) The `assumed temperature' method of reducing thrust
to suit take-off weight does so at constant thrust/weight
ratio, and the actual take-off distance, take-off run and
accelerate-stop distances at reduced thrust are less than
at full thrust and full weight by approximately 1 % for
every 3°C that the actual temperature is below the assumed
temperature.
(b) The accelerate-stop distance is further improved by the
increased effectiveness of full reverse thrust at the lower
temperature.
(c) The continued take-off after engine failure is protected
by the ability to restore full power on the operative engines.
Furthermore, although there is inevitably a slight increase
in average risk, this increase is minimised by two factors:
(a) A significant percentage of take-offs are at weights close
enough to R.T.O.W. not to warrant the use of reduced thrust.
(b) The excess margins on lighter-weight take-offs are largely
preserved by the maximum thrust reduction rule.
In any case it is anticipated that more than adequate
compensation will be provided by enhanced engine reliability.
--------------------------------------------------------------

BTW Gord, just in case you are not that familiar with civilian
jet transports, takeoff thrust does not equate to full throttle.
T.O. thrust is set in acordance with pressure/temperature charts
always with some throttle left to account for the hot/high day.


Bob Moore
VP-21 VP-46
ATP B-707 B-727
PanAm (retired)

Bob Moore wrote:
--------------------------------------------------------------

BTW Gord, just in case you are not that familiar with civilian
jet transports, takeoff thrust does not equate to full throttle.
T.O. thrust is set in acordance with pressure/temperature charts
always with some throttle left to account for the hot/high day.


Bob Moore

Very interesting Bob, thanks. I certainly won't be arguing with
HIM any time soon and yes, I'm familiar with less than full
throttle 'full power'. I'm very familiar with large radial recips
most of which have very definite power limits well short of the
firewall. But we always used those limits no matter what
conditions prevailed and I didn't know that large jet a/c used
anything less. I gather that the 747 freighter loss at Halifax
Canada had approx. the proper weight calculated but that It was
some 55 Km PH low in speed and that there was some controversy as
to whether he had used the whole runway.

--

-Gord.
(use gordon in email)