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B737-low N1 during take off roll could mean trouble. .

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B737-low N1 during take off roll could mean trouble. .

Old 23rd Oct 2018, 14:34
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B737-low N1 during take off roll could mean trouble. .

https://www.skybrary.aero/index.php/B738,_Belfast_International_UK,_2017?utm_source=SKYbrary&utm _campaign=ad274eb84b-604_Validation_Data_21_10_2018&utm_medium=email&utm_term=0_e 405169b04-ad274eb84b-276530305

It is good airmanship to always check the N1 for "reasonable-ness" during early part of the take-off run.

Last edited by Tee Emm; 24th Oct 2018 at 01:54.
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Old 24th Oct 2018, 01:37
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Thanks for posting - interesting read!
The Skybrary summary doesn't report the experience of the FO - how could you mix up the "Expected TOPC temp" with the ambient temp on the ground?? (-52 vs 16 degs)
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Old 24th Oct 2018, 03:36
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I should have said I'm not familiar with a 737 FMS - is the Expected TOPC Temp on the same page as the ground temp?
Expected TOPC Temp is not something I've used before...
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Old 24th Oct 2018, 03:37
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"Excuse me skipper, since we're not going anywhere fast, may I suggest we put the throttles into the full forward position?!"
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Old 24th Oct 2018, 08:49
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This is mind blowing. They noticed the “slow acceleration” before rotation and “very shallow clim” but they didn’t put the throttles full forward until they were 800 feet aal.
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Old 24th Oct 2018, 08:54
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Originally Posted by Skipname View Post
This is mind blowing. They noticed the “slow acceleration” before rotation and “very shallow clim” but they didn’t put the throttles full forward until they were 800 feet aal.
This is indeed amazing. I'd say that checking the throttles when not getting expected performances is pretty basic airmanship.
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Old 25th Oct 2018, 01:07
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Originally Posted by Skipname View Post
This is mind blowing. They noticed the “slow acceleration” before rotation and “very shallow clim” but they didn’t put the throttles full forward until they were 800 feet aal.
Skipname,
Maybe there was not a published SOP in the "manual" by whatever name, and woe betide any pilot who exercises initiative outside of SOPs.
And--- too many full rated power applications will have a $$$ effect on the engine warranty.
It is often quite difficult to find "airmanship/common sense" in the QRH index of many CASA micro-managed operators.
Tootle pip!!
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Old 25th Oct 2018, 02:42
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Originally Posted by Skipname View Post
This is mind blowing. They noticed the “slow acceleration” before rotation and “very shallow clim” but they didn’t put the throttles full forward until they were 800 feet aal.
The guys who put the 737 into the Potomac didn't put the throttles full forward ever......
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Old 25th Oct 2018, 12:42
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Originally Posted by LeadSled View Post
Skipname,
Maybe there was not a published SOP in the "manual" by whatever name, and woe betide any pilot who exercises initiative outside of SOPs.
And--- too many full rated power applications will have a $$$ effect on the engine warranty.
It is often quite difficult to find "airmanship/common sense" in the QRH index of many CASA micro-managed operators.
Tootle pip!!
I have no experience in CASA land and I am aware that there are a number of operators world wide who's attitudes towards flying are reducing the safety factor and forces the pilots to apply the SOPs to the letter instead of using common sense. However I think in the above mentioned incident not applying common sense could have resulted in a serious accident, they were very lucky.

In my current outfit, an EASA operator, on the introduction page of the operations manual there is a paragraph that goes something like "as it is impossible to foresee all kinds of emergencies and cover them in this manual, we encourage pilots to use their knowledge, experience and common sense while applying the procedures stated in this manual".
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Old 26th Oct 2018, 08:20
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Originally Posted by Skipname View Post
In my current outfit, an EASA operator, on the introduction page of the operations manual there is a paragraph that goes something like "as it is impossible to foresee all kinds of emergencies and cover them in this manual, we encourage pilots to use their knowledge, experience and common sense while applying the procedures stated in this manual".
Skipname,
Sound familiar from a Boeing manual, and severely disapproved of by a certain kind of CASA Flying Operations Inspector ---- who even demand the manufacturer's QRH expanded so that it is certainly no longer quick.

Some years ago, Qantas had an A330 horsing all over the sky due to a very obscure (it has not been positively identified to this day) ADC fault, north of Perth.
The reaction of the Captain was to disconnect the AP and "fly the aeroplane". I am certain most of us would have done the same. Dig up the interview with the Captain after he retired, the "official" version does not really get across how the aircraft was behaving.

I was part of a discussion in CASA Canberra, shortly after, where more than one chair-borne FOI, none with A330 (or any large aircraft) experience, was pushing for the Captain to be suspended, pending action against his license, for non-adherence to the SOPs, as, in their view, in their chosen "appropriate QRH procedure" disconnecting the AP came "down the list" after checking circuit breakers and a few other bits and pieces ---- which, given the recorded behavior of the aeroplane, may almost certainly have been physically impossible.

As you may well imagine, my "firmly" expressed views were not, at the time, "acceptable to CASA" in the "official" position taken by these two "CASA operations experts".

Tootle pip!!

Last edited by LeadSled; 26th Oct 2018 at 08:20. Reason: typo
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Old 26th Oct 2018, 08:31
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Devil

my "firmly" expressed views were not, at the time, "acceptable to CASA" in the "official" position
Let me guess, Leadsled.
I assume that after passing comments on the dubiousness of their ancestry, you probably also mentioned that in your view they had had recent brain surgery, which was unsuccessful, and that they should consider not involving themselves in the issue any further.

If not, you probably should have!
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Old 26th Oct 2018, 13:16
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Low N1

Originally Posted by Skipname View Post
This is mind blowing. They noticed the “slow acceleration” before rotation and “very shallow clim” but they didn’t put the throttles full forward until they were 800 feet aal.
This to me says that the reliance of automation of systems has, and probably will continue to do so, lead to a loss of crew awareness of how the aeroplane actually works. The first
reaction to slow acceleration should have been to check the thrust. Not noticing the low setting until 800' agl is gross unawareness by the crew and they should have their backsides
well and truly kicked.
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Old 26th Oct 2018, 15:22
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The guys who put the 737 into the Potomac didn't put the throttles full forward ever......


Readers of that accident may recall that ice had blocked the Pt2 sensors. In turn, this caused the EPR gauges to over-read. The pilots did not notice that the N1 indication was significantly lower than rated take off thrust because the pilots had set planned takeoff EPR unaware the EPR readings were erroneous. In those days on the P&W JT8D engines, EPR was the primary means of setting take off power despite EPR being prone to erroneous indications under certain weather conditions.
See: https://en.wikipedia.org/wiki/Air_Florida_Flight_90.

Comments have been made about the lack of action by the crew of the Sunwing 737-800 which departed from Belfast in day VMC. Some readers were of the opinion that the crew should have noticed the lack of acceleration associated with the low N1 and done something about it. Maybe so.

This
writer was involved with a similar incident on Nauru in the 1980's where erroneous EPR indications caused by partially blocked PT2 sensors caused both engines EPR to over-read simultaneously. The take off was at night and the runway length 5600 feet with no overrun safety area. The runway end finished up in a boulder strewn small cliff leading to a drop into the sea.The three pilots up front failed to pick the initially slow acceleration in the early part of the take off roll; possibly because the slight reduction of power was equivalent to a normal reduced thrust rate of acceleration. If the runway had been longer the incident would not have been immediately apparent.

But a ten percent reduction of thrust (N1) on a limited length runway, coupled with seemingly correct EPR (erroneous indication as it transpired) was potentially deadly, as it nearly turned out.
During the whole take off roll, the engine instruments (EPR, N1, fuel flow, engine oil temps and pressures) showed parallel needle indications as both engines were performing exactly as expected. Both EPR needles were 2.18 EPR corresponding to max bleeds off thrust. Due to the dim lighting required for the night take off, the difference between the expected 100 percent N1 and the actual 90 percent N1 shown on the gauges, was about 6 mm or less than the width of a needle and needed more than just a quick glance.

It wasn't until there were about five runway lights to go did it become apparent that VR was not going to be reached before the end of the runway. At VR minus 15 knots the captain took control from the PF and simultaneously "firewalled" the throttles and rotated early to get airborne before the runway end. Any late abort (we were still below V1) would have been disastrous and we would have gone off the cliff.


The point that stuck in my mind is that no one picked the less than expected acceleration, either early in the take off roll or later in the take off roll, until it suddenly dawned that with only a few runway lights to go we were never going to get airborne by the end of the runway. . Yet, throughout the take off run, all the engine instruments including the vital EPR gauges showed normal settings. They included the N1 needles; except closer scrutiny during the take off roll would have revealed slightly lower N1 than expected and planned. It was because all gauges looked normal throughout he take off roll. In hindsight, it was all too easy to blame the crew for not picking the small difference in N1 from the planned setting..

With
the same operator there had been two earlier instances when the PT2 sensor on one engine was blocked by foreign objects. In that, case one EPR needle was seen to suddenly increase its reading well beyond the planned maximum setting and the split between the two EPR's were quickly noticed by the time the aircraft reached 80 knots. At 100 knots the F/O tried to throttle back that engine to equalise the EPR readings but was prevented by the captain who directed the F/O to set equal N1 and ignore the faulty EPR reading. But in the incident described earlier, there was no split between the EPR or the N1 gauges because both PT2 sensors of the engines were blocked and thus nothing obvious to a quick glance during the take off roll was noticed. The blockage of the Pt2 sensors was caused by a combination of phosphate dust from the nearby mine and insects that had nested in the tube sensors.

The point of this story is this: At night especially, degraded aircraft acceleration (for whatever reason) may not be immediately apparent until the departure end of the runway is approaching fast and it becomes obvious the aircraft is committed to go; even if it means early rotation and fire-walling the throttles.

Last edited by Centaurus; 26th Oct 2018 at 15:33.
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Old 27th Oct 2018, 05:02
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Originally Posted by Pinky the pilot View Post
Let me guess, Leadsled.
I assume that after passing comments on the dubiousness of their ancestry, you probably also mentioned that in your view they had had recent brain surgery, which was unsuccessful, and that they should consider not involving themselves in the issue any further.

If not, you probably should have!
Pinky,
Pretty close, and definitely not couched in the usual obfuscating bureaucratese. There were also references bovines and to other parts of the standard anatomy!!
Tootle pip!!

PS: Always a good idea to know (and check) the N1 when EPR is set ----- after all "thrust set" is thrust set, not just EPR.

Last edited by LeadSled; 27th Oct 2018 at 05:06. Reason: ps added.
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Old 27th Oct 2018, 06:20
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In thrust we trust.

( With thanks to Pratt and Whitney ).
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