Simple question on old 747SP incident...

[wrench1]

If the #1 engine had been retarded to match the low thrust #4 engine, would the aircraft have remained level? Not passing judgement just curious.
https://www.thisdayinaviation.com/19-february-1985/

[megan]

Would remain wings level but would descend due lack of overall thrust, forgetting about engaged autopilot modes. Depending on engaged autopilot modes it may be possible for the aircraft to maintain altitude and deaccelerate to the point of stalling..

[LeadSled]

If the #1 engine had been retarded to match the low thrust #4 engine, would the aircraft have remained level? Not passing judgement just curious.
https://www.thisdayinaviation.com/19-february-1985/

The core issue was inattention --- nobody "flying the aeroplane".
Everybody concentrating on "the problem", at the expense of "Rule 1- Fly the Aeroplane".
The way that story is written gives a wrong impression of how the control was lost, refer to the original accident report for what really happened.
Speaking as somebody who took a great interest, as I was flying SPs at the time.
Tootle pip!!

[4 Holer]

Lead you were probably flying RR power a different animal to the JT9-7AH with a mind of its own if the bleeds are off or water/ice in the EVC vain control up and down and power shift all day long.

We would bring it back to part power trimmed the airplane and see how it behaved. At the same time requested decent say 360 to 320 dependent of weight and current altitude or a lower altitude off the FE chart once in the drift down. If the #1 didn't behave bring back to flight idle and leave it there. At flight idle if still mis behaving shutdown and advise ATC #1 shutdown and proceeding 3 engine normal operations and update you new weigh point times . At all stages trimming off the thrust reduction with right rudder ( ball in centre ) and bumping the remaining engines up a little on the power dependent on the weights. The SP would fly fine on 3 motors no need to panic grab another coffee and press on if you have the available gas.

[TURIN]

4 holer are you sure about that?

[tdracer]

If the #1 engine had been retarded to match the low thrust #4 engine, would the aircraft have remained level? Not passing judgement just curious.
https://www.thisdayinaviation.com/19-february-1985/

Yes, but all they really needed to do was disconnect the autothrottle autopilot, and retrim the aircraft for the thrust imbalance. LeadSled is correct - nobody was flying the aircraft - they were all busy trying to start an engine while thousands of feet above the restart envelope while expecting the autopilot to do something it was never intended to do. By design, the autopilot on the the older 747s didn't have enough authority to overcome an outboard engine power loss - so that an autopilot hard over would be no worse than an engine failure (remember, we're talking 1970s vintage analog electronics).

[lomapaseo]

does not the autopilot come into this by trying to maintain altitude and thus let the aircraft slow down and/or roll into a weak engine?

[tdracer]

Yea lomapaseo - I've edited to fix - I was thinking autopilot but wrote autothrottle and didn't catch the error until I read your post and wondered why you were repeating me....

[mustangsally]

Some basic training is amiss! Using roll control to counteract to correct the situation was a mistake. The rudder should have been the primary control input to correct the situation. Even if the unresponsive engine was at idle thrust there should have been more than enough rudder to keep the aircraft flying straight at flight level (this was a Boeing not an Airbus) or maybe a slow decent to three engine flight level. One would need the charts to confirm what the allowable three engine flight level would have been. I doubt that it could have maintained FL 410, all dependent on temperature and weight. A quick think back tells me that the two engine FL would have been most likely either side of FL 210, or maybe a bit lower. Retarding the other outboard was a big mistake. With two engines producing thrust and two at idle the aircraft will have to start descending. Check the drift down chart for what the target speed would be and adjust as altitude drops and the aircraft will level off on its own when that FL has been reached.

I have not read the full report, but using the autopilot with altitude hold and lots of roll control only compounded the problem.

One of the other problems comes from all of our cultures. The senior officer (oldest) is always right. This happened a long time ago, and maybe we have all learned that each crew member has an input and all suggested should be considered.

[DaveReidUK]

NTSB Aircraft Accident Report: China Airlines Boeing 747-SP, N4522V 300 nautical miles NW of San Francisco, CA February 19, 1985 (https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR8603.pdf)

[mustafagander]

The short answer to your question wrench1 is yes. But, and a big BUT, the aircraft would have stalled anyway.
I have a bit of time on B747 of all types, -100, -200, -300, -SP, -400. Now this SP was behaving exactly as advertised, Nav Mode INS, ALT Hold will always give this result with a high altitude engine failure unless crew takes action fairly quickly.
I was FEO on SP but in all my time operating jets at high altitude we always knew the 3 eng alt, always. Most of us kept it updated on our notepad and some Cpt required it on the pedestal behind the TL updated half hourly.
Eng failure triggered an automatic response from the crews in my airline that we have just a few minutes before we descend.
This incident shows the crew in a very poor light. Fatigue excuses accepted but the flight crew is responsible to be able to safely operate the aircraft, if not don't go. Yes, to answer the obvious question, I have personally pulled the pin due to fatigue.

[LeadSled]

Lead you were probably flying RR power a different animal to the JT9-7AH with a mind of its own if the bleeds are off or water/ice in the EVC vain control up and down and power shift all day long.
.

4 Holer,
Gee, thanks for that, didn't notice that the SPs I was flying had Rollers- I will pay more attention next time.

Seriously, if you took the trouble to read the actual accident report, perhaps ( I don't know your real aviation experience, if any) you would realise that what happened --- IN LOSING CONTROL ---- had nothing to do with what engines were fitted, a 747SP with Rollers would have done the same thing.

They were all head down, frigging around with "THE PROBLEM", nobody flying the aeroplane.

And, by the way, I have plenty of time nursing various JT-9 from the -3A through various iterations of the -7, up to the JT-9D-7RE, including quite a bit of relevant hands-on "experience" of the bleed system, also the behavior of the HP fuel pumps and the results for the VIGV controllers.

As a consequence, I much preferred the CF6/80-C2 in the various thrust ratings I used it.

Tootle pip!!

[India Four Two]

but neither pilot or copilot applied any rudder inpbut neither pilot or copilot applied any rudder inputs to correct the yaw. (It was later determined that they believed, incorrectly, that the autopilot controlled rudder position.

Unebelievable. An incompetent crew. Did they fly again?

a peak 5.1 Gs at 19,083 feet

Over 5 G in a commercial jet. I imagine the passengers thought they were going to die and I guess they very nearly did.

What’s the ultimate load factor for a 747 SP?

[Retired DC9 driver]

Years ago I saw that same 747 SP with the shredded elevators on the ramp in SFO. It got my attention..

Much later on a 767-200 flight; my leg, level at FL410 , coming North from Barbados at night, the airspeed was slowly decreasing, and I noticed the yoke slowly rolling to the right ! I immediately remembered the China Air incident.
Checked the engine instruments, and (small EPR gauges on EFIS) left engine had rolled back to zero thrust. Generator still on line; I disconnected the autopilot, and started a drift down to engine out altitude, EO driftdown speed came up as 217 K , but no way I was going to bring speed back that far. I wanted more rudder authority. We were manoeuvring around some TCU in the descent too so I hand flew it while the Capt. did the checklist..
Engine was surging in descent, but by FL 370 or so it had recovered. Never had to shut it down, EGT didn't rise..

[sb_sfo]

I had a view out my office window of the aircraft after it arrived in SFO and was towed off to remote parking. Taking a look from the ground, it was apparent to me that the APU mounts failed somewhere below 5.1 Gs. Never got a look at the interior, but I heard it was trashed.

[MarkerInbound]

Over 5 G in a commercial jet. I imagine the passengers thought they were going to die and I guess they very nearly did.

What’s the ultimate load factor for a 747 SP?

More than 5.1. The aircraft was repaired and returned to service with a little extra wing dihedral.