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THS Jackscrew design

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THS Jackscrew design

Old 14th Jan 2013, 21:33
  #21 (permalink)  
 
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i thought there were some other issues with alaska mx...a ''home made tool to judge tolerance'', a different lubrication than mfr rec'd.

just a lesson for all pilots...its up to you if the flight is safe or not. not some guy in maintenance control or ''dispatch''.

dispatch...ha...I got a message during landing rollout on a snowy runway at KSYR...it came on ACARS after we landed...message follows: DO NOT LAND AT KSYR.

our message in response, once we had stopped was...DO YOU WANT US TO TAKEOFF AGAIN?

dispatch.!
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Old 14th Jan 2013, 22:09
  #22 (permalink)  
 
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Originally Posted by sevenstrokeroll View Post
i thought there were some other issues with alaska mx...a ''home made tool to judge tolerance'', a different lubrication than mfr rec'd.
In general yes, but no evidence of that on the accident airframe. For bringing the general lapses in maintenance practice to light, the whistleblower concerned never worked in aviation again.
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Old 15th Jan 2013, 00:36
  #23 (permalink)  
 
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No Dozy, your wrong. Read the report. The threads were becoming more and more stripped. So when the pilots trimmed for an altitude, it would hold, then give...then they needed to retrim for the next place that held...this went on and on and on, until such time trim wouldn't cover the problem, then slop in the tail became so great and where it would hold at a weakened thread, then give, then hold, then give, until there wasn't any threads in which to hold, thus loosing control. So ponder this as the pilots, Alaska's finest, top notch guys, hired from the top of resume pile, went through all the checklists (ooos no tail control failure)...SOPS(ooops no jack screw failure)..Dispatch (gosh we don't know...just keep flying to LA) and lastly the pilots yanking back and forth on the yoke trying to keep the plan upright, flip it over into the ocean. You can call this mechanical failure but it's actually top down from the Chief Pilot and HR, people I have met. If you hire mechanics that don't do inspections and robots that can't make a decision these problems will happen from time to time. Another great example of CRM at work by the way.
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Old 15th Jan 2013, 01:04
  #24 (permalink)  
 
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the robe

I tend to agree with your views...but the crew was told to continue past LA...I think either to San Francisco or Seatle...memory fails me now.

Each accident, if remembered by another crew may save another flight.

And, like I said...call dispatch after you land...they really don't know too much. IF THEY DID< THEY WOULD FLY THE PLANE and YOU WOULD CLEAN IT
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Old 15th Jan 2013, 02:57
  #25 (permalink)  
 
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Seven - Thanks for correcting me, your right, they lost it around SFO on the way up North.
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Old 15th Jan 2013, 07:10
  #26 (permalink)  
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No Dozy, your wrong. Read the report. The threads were becoming more and more stripped. So when the pilots trimmed for an altitude, it would hold, then give...then they needed to retrim for the next place that held...this went on and on and on, until such time trim wouldn't cover the problem, then slop in the tail became so great and where it would hold at a weakened thread, then give, then hold, then give, until there wasn't any threads in which to hold, thus loosing control.
I'm sorry, where did you find such detailed reports to prove that pilots have made such exageratted attempts until all the threads wore out?

In all reports I found there are no detailed actions to prove this. I think everyone agrees that they would have to land soon, but it makes me think that the system gave it because then no longer have what to keep it in place, not as they would have spent time on it to totally wear it out. As someone here pointed, It wasn't a gradual thing, it was stuck - literally held in place by a sliver of metal. Once that went there was nothing they could do.

What if an aircraft lost good data from sensors, and cycled elevator and THS automatically, to twelve degrees pitch down, at the same time disallowing manual override?
Uncontrollable. Loss of Control. Program Error.
Those computers do not have a shutdown button?

the jackscrew assembly failed and due to either inadequate or non existent limit stops, the horizontal tail went well past limits,
In my opinion, this is one of the most important aspects in this case.

I agree it is such a stupid idea to contact MX inflight, what I think is more important is how it comes to trust MX regarding installation and correct rigging?

Last edited by David36; 15th Jan 2013 at 07:14.
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Old 15th Jan 2013, 14:47
  #27 (permalink)  
 
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The issue of "design fault" was raised a few posts back. I might agree in terms of the maintainability of the jackscrew. Pulling a ladder or scaffold to reach the stab isn't exactly the easiest sometimes.

OTOH one failure over the decades doesn't exactly shout "bad design" when dozens of other operators had minimal issues with the jackscrew. The finger definitely seems to point to the operator in this case.

BTW, the accident occurred off Santa Barbara, past LAX on the way to SFO.
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Old 15th Jan 2013, 17:44
  #28 (permalink)  
 
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Originally Posted by David36 View Post
Those computers do not have a shutdown button?
No, but with Airbus FBW the pilot can override automatic trim by setting the trim manually with the trim wheel and holding it there. The hard-alpha protections can be disabled by shutting off 2 of the ADR computer modules.

Obviously this is outside of recommended procedure, but on the flip side it's a potential solution for an extremely rare occurrence. It's also way off the topic for this thread, but given the source of the query that's no surprise...

@barit1 : The design met the certification requirements for the time. I believe they've since been tightened...

Last edited by DozyWannabe; 15th Jan 2013 at 17:46.
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Old 17th Jan 2013, 04:23
  #29 (permalink)  
 
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Years ago I had the same problem with a jammed brake on one side (policy to test the brakes prior to landing and one stuck fully on). Pedal was hard and could not release it.
Called Maintenance and they said take the crash axe and break the servo hydraulic line (described to me) to release the pressure. It took me 45 minutes due to the confined space but it worked.
Sometimes they give good advice. Just saying.
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Old 17th Jan 2013, 07:27
  #30 (permalink)  
 
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No Dozy, your wrong. Read the report. So when the pilots trimmed for an altitude, it would hold, then give...then they needed to retrim for the next place that held...this went on and on and on, until such time trim wouldn't cover the problem,
Wrong. Read the report.
FDR data indicated that the horizontal stabilizer’s last movement during the climbout was to 0.4 airplane nose down at 1349:51 as the airplane was climbing through 23,400 feet at 331 knots indicated airspeed (KIAS). After this, no horizontal stabilizer movement was recorded on the FDR until the airplane’s initial dive 2 hours and 20 minutes later.
The passengers had the wrong pilots that day
Absolute nonsense. You can sit in your lounge chair as a non pilot and Monday morning quarter back the decisions made by the crew with 20/20 hindsight, but I venture any typical line crew probably would have made the same decisions.
2.2.5 Flight Crew Decision-Making
2.2.5.1 Decision to Continue Flying Rather than Return to PVR

Safety Board investigators considered several reasons that might explain the captain’s decision not to return immediately to PVR after he experienced problems with the horizontal stabilizer trim system during the climbout from PVR.

Neither the Alaska Airlines MD-80 Quick Reference Handbook (QRH) Stabilizer
Inoperative checklist nor the company’s QRH Runaway Stabilizer emergency checklist required landing at the nearest suitable airport if corrective actions were not successful. These checklist procedures were the only stabilizer-related checklist procedures contained in the QRH, and the flight crew most likely followed these checklist procedures in their initial attempts to correct the airplane’s jammed stabilizer

The airplane’s takeoff weight of 136,513 pounds was well below the takeoff and climb limits for the departure runway, but it exceeded the airplane’s maximum landing weight of 130,000 pounds. Because the airplane did not have an in-flight fuel dumping system, the airplane would have had to remain in flight for about 45 minutes after takeoff until enough fuel had burned to reduce the airplane’s weight by the 6,500 pounds needed to reach the airplane’s maximum landing weight. A return to PVR to execute an overweight landing would have required higher than normal approach speeds for landing and would have created additional workload and risk. An overweight landing at PVR would have been appropriate if the flight crew had realized the potentially catastrophic nature of the trim anomaly. However, in light of the airplane’s handling characteristics from the time of the initial detection of a problem to the initial dive, the flight crew would not have been aware that they were experiencing a progressive, and ultimately catastrophic, failure of the horizontal stabilizer trim system.

The flight crew would have been aware that Alaska Airlines’ dispatch and
maintenance control in Seattle-Tacoma International Airport (SEA), Seattle, Washington, and LAX could be contacted by radio (via ground-based repeater stations) when the airplane neared the United States. However, even though the last horizontal stabilizer trimming movement was recorded by the FDR about 1349:51, the flight crew did not contact Alaska Airlines’ maintenance until shortly before the beginning of the CVR transcript about 1549,225 which suggests that control problems caused by the jammed horizontal stabilizer remained manageable for some time. Further, as previously mentioned, the positive aerodynamic effects of the higher cruise airspeed and fuel burn would have reduced the necessary flight control pressures to roughly 10 pounds and made the airplane easier to control. Therefore, the Safety Board concludes that, in light of the absence of a checklist requirement to land as soon as possible and the circumstances confronting the flight crew, the flight crew’s decision not to return to PVR immediately after recognizing the horizontal stabilizer trim system malfunction was understandable.

Although they elected not to return to PVR, later in the flight the flight crew
decided to divert to LAX, rather than continue to San Francisco International Airport (SFO), San Francisco, California, where the flight was originally scheduled to make an intermediate stop before continuing to SEA. Comments recorded by the CVR indicated that the flight crew may have felt pressure from Alaska Airlines dispatch personnel to land in SFO.227 However, after discussing the malfunctioning trim system and current and expected weather conditions at SFO and LAX with Alaska Airlines dispatch and maintenance personnel, the captain decided to land at LAX rather than continue to SFO. The decision to divert to LAX was apparently based on several factors, including more favorable wind conditions at LAX (compared to a direct crosswind at SFO) that would reduce the airplane’s ground speed on approach and landing228 and the captain’s concern, expressed to Alaska Airlines dispatch personnel, about “overflying suitable airports.” The Safety Board concludes that the flight crew’s decision to divert the flight to LAX rather than continue to SFO as originally planned was prudent and appropriate. Further, the Safety Board concludes that Alaska Airlines dispatch personnel appear to have attempted to influence the flight crew to continue to SFO instead of diverting to LAX.
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Old 17th Jan 2013, 09:25
  #31 (permalink)  
 
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Brian - Maybe you should read you own report. Simply put it's not like they were flying along and all of a sudden the tail fell off. They were having trim and flight control problems for an hour, hence the call to dispatch.

Apologize all you want for the pilots...but it was a top down culture at Alaska that caused this issue...from mechanics that didn't do inspections to pilots who couldn't make a decision and would fly into a mountain if dispatch told them to.
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Old 17th Jan 2013, 09:28
  #32 (permalink)  
 
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pilots who couldn't make a decision and would fly into a mountain if dispatch told them to
So do tell what request/order from dispatch did they comply with?
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Old 17th Jan 2013, 09:42
  #33 (permalink)  
 
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The fact that they screwed with their trim for an hour then called dispatch for a 'what do we do?' is the point Brian.
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Old 17th Jan 2013, 11:17
  #34 (permalink)  
 
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They did not make a request for "'what do we do". They elicited information as would any crew and made their own decisions with respect to the information received.

According to Alaska Airlines documents, ATC and CVR information, and postaccident interviews with Alaska Airlines dispatch and maintenance personnel, the flight crew contacted the airline’s dispatch and maintenance control facilities in SEA some time before the beginning of the CVR transcript at 1549:4912 to discuss a jammed horizontal stabilizer and a possible diversion to Los Angeles International Airport (LAX), Los Angeles, California. These discussions were conducted on a shared company radio frequency between Alaska Airlines’ dispatch and maintenance facilities at SEA and its operations and maintenance facilities at LAX.

At 1549:56, the autopilot was disengaged; it was re-engaged at 1550:15.
According to the CVR transcript, at 1550:44, SEA maintenance asked the flight crew, “understand you’re requesting… diversion to LA …is there a specific reason you prefer LA over San Francisco?” The captain replied, “well a lotta times its windy and rainy and wet in San Francisco and uh, it seemed to me that a dry runway…where the wind is usually right down the runway seemed a little more reasonable.

At 1552:02, an SEA dispatcher provided the flight crew with the current SFO
weather (wind was 180 at 6 knots; visibility was 9 miles). The SEA dispatcher added, “if uh you want to land at LA of course for safety reasons we will do that…we’ll …tell you though that if we land in LA… we’ll be looking at probably an hour to an hour and a half we have a major flow program going right now.” At 1552:41, the captain replied, “I really didn’t want to hear about the flow being the reason you’re calling us cause I’m concerned about overflying suitable airports.” At 1553:28, the captain discussed with the first officer potential landing runways at SFO, stating, “one eight zero at six…so that’s runway one six what we need is runway one nine, and they’re not landing runway one nine.” The first officer replied, “I don’t think so.” At 1553:46, the captain asked SEA dispatch if they could “get some support” or “any ideas” from an instructor to troubleshoot the problem; he received no response. At 1555:00, the captain commented, “it just blows me away they think we’re gonna land, they’re gonna fix it, now they’re worried about the flow, I’m sorry this airplane’s [not] gonna go anywhere for a while …so you know.” A flight attendant replied, “so they’re trying to put the pressure on you,” the captain stated, “well, no, yea.”

At 1556:08, the SEA dispatcher informed the flight crew that, according to the SFO automatic terminal information service, the landing runways in use at SFO were 28R and 28L and that “it hasn’t rained there in hours so I’m looking at…probably a dry runway.” At 1556:26, the captain stated that he was waiting for a requested center of gravity (CG) update (for landing), and then he requested information on wind conditions at LAX. At 1556:50, the SEA dispatcher replied that the wind at LAX was 260 at 9 knots.

Nine seconds later, the captain, comparing SFO and LAX wind conditions, told the SEA dispatcher, “versus a direct crosswind which is effectively no change in groundspeed…I gotta tell you, when I look at it from a safety point I think that something that lowers my groundspeed makes sense.”16 The SEA dispatcher replied, “that’ll mean LAX then for you.” He then asked the captain to provide LAX operations with the information needed to recompute the airplane’s CG because “they can probably whip out that CG for you real quick.” At 1558:15, the captain told the SEA dispatcher, “we’re goin to LAX we’re gonna stay up here and burn a little more gas get all our ducks in a row,
and then we’ll uh be talking to LAX when we start down to go in there.” At 1558:45, the captain asked LAX operations if it could “compute [the airplane’s] current CG based on the information we had at takeoff.”

At 1602:33, the captain asked LAX operations for wind information at SFO. LAX operations replied that the winds at SFO were 170 at 6 knots. The captain replied, “that’s what I needed. We are comin in to see you.” At 1603:56, the first officer began giving LAX operations the information it needed to recompute the airplane’s CG for landing.

At 1607:54, a mechanic at Alaska Airlines’ LAX maintenance facility contacted
the flight crew on the company radio frequency and asked, “are you [the] guys with the uh, horizontal [stabilizer] situation?” The captain replied, “affirmative,” and the mechanic, referring to the stabilizer’s primary trim system, asked, “did you try the suitcase handles and the pickle switches?” At 1608:03, the captain replied, “yea we tried everything together.” At 1608:08, the captain added, “we’ve run just about everything if you’ve got any hidden circuit breakers we’d love to know about ‘em.” The mechanic stated that he would “look at the uh circuit breaker uh guide just as a double check.” The LAX mechanic then asked the flight crew about the status of the alternate trim system, and, at 1608:35, the captain replied that “it appears to be jammed…the whole thing, it [the AC load meter] spikes out when we use the primary, we get AC [electrical] load that tells me the motor’s tryin to run but the brake won’t move it. when we use the alternate, nothing happens.”

At 1608:50, the LAX mechanic asked, “you say you get a spike…on the meter up there in the cockpit when you uh try to move it with the …primary right?” According to the CVR transcript, at 1608:59, the captain addressed the first officer before responding to the mechanic, stating, “I’m gonna click it off you got it.” One second later, the first officer replied, “ok.” At 1609:01, the captain reiterated to the LAX mechanic that the spike occurred “when we do the primary trim but there’s no appreciable uh change in the uh electrical uh when we do the alternate.” The LAX mechanic replied that he would see them when they arrived at the LAX maintenance facility.
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Old 18th Jan 2013, 00:56
  #35 (permalink)  
 
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No your right Brian, when the flight controls are failing, a crew calls up dispatch to talk to let the chief pilot know to have catering ready when they land.
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Old 18th Jan 2013, 03:37
  #36 (permalink)  
 
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No your right Brian, when the flight controls are failing, a crew calls up dispatch to talk to let the chief pilot know to have catering ready when they land.
You're a jerk (first class), but almost forgivable in a non pilot such as yourself. They did no such thing, as the dialogue of discussion with dispatch I posted above proves.

Lets have a look at the reports discussion re failing controls. I absolutely hate introducing facts into the discussion.
The Safety Board recognizes that, from an operational perspective, the flight crew could not have known the extent of airplane damage. Although flight crews are trained in jammed stabilizer and runaway stabilizer scenarios, the loss of acme nut and screw engagement exceeded any events anticipated in emergency training scenarios, and the flight crew was not trained to devise or execute appropriate configurations and procedures to minimize further damage to the airplane or to prevent the accident. However, the flight crew’s earlier attempts to activate the trim motor and configuration changes may have worsened the situation. As previously discussed, the captain’s activation of the primary trim motor at 1609:16 precipitated the release of the jam and the initiation of the initial dive. However, it was not clear how many times previous to that the flight crew activated the primary trim motor nor was it clear whether or to what extent the prior activations hastened the release of the jam. Therefore, the Board could not determine the extent to which the activation of the primary trim motor played a role in causing or contributing to the accident.
2.2.5.5 Adequacy of Current Guidance

The Safety Board notes that after the flight 261 accident, Boeing issued a flight operations bulletin outlining procedures to be followed in the event of an inoperative or malfunctioning horizontal stabilizer trim system. The bulletin advised flight crews to

complete the flight crew operating manual (FCOM) checklist(s). Do not attempt additional actions beyond that contained in the checklist(s). If completing the checklist procedures does not result in operable trim system, consider landing at the nearest suitable airport.

The Safety Board agrees that this advice is generally appropriate. However, the Board does not agree that the flight crew should merely “consider” landing at the nearest suitable airport if accomplishing the checklist items does not result in an operational trim system. In such a case, the flight crew should always land at the nearest suitable airport as expeditiously and safely as possible. Further, the bulletin provides additional information regarding the possibility that repeated or continuous use of the trim motors may result in thermal cutoff and states that the motor may reset after a cooling period. The Board is concerned that this additional information addressing repeated or continuous use of the trim motors may weaken or confuse the initial guidance to refrain from attempting troubleshooting measures beyond those specified in the checklist procedures.

The Safety Board concludes that, without clearer guidance to flight crews
regarding which actions are appropriate and which are inappropriate in the event of an inoperative or malfunctioning flight control system, pilots may experiment with improvised troubleshooting measures that could inadvertently worsen the condition of a controllable airplane. Accordingly, the Safety Board believes that the FAA should issue a flight standards information bulletin directing air carriers to instruct pilots that in the event of an inoperative or malfunctioning flight control system, if the airplane is controllable they should complete only the applicable checklist procedures and should not attempt any corrective actions beyond those specified. In particular, in the event of an inoperative or malfunctioning horizontal stabilizer trim system, after a final determination has been made in accordance with the applicable checklist that both the primary and alternate trim systems are inoperative, neither the primary nor the alternate trim motor should be activated, either by engaging the autopilot or using any other trim control switch or handle. Pilots should further be instructed that if checklist procedures are not effective, they should land at the nearest suitable airport.The Safety Board also believes that the FAA should direct all Certificate Management Offices (CMO) to instruct inspectors to conduct surveillance of airline dispatch and maintenance control personnel to ensure that their training and operations directives provide appropriate dispatch support to pilots who are experiencing a malfunction threatening safety of flight and instruct them to refrain from suggesting continued flight in the interest of airline flight scheduling.
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Old 18th Jan 2013, 21:15
  #37 (permalink)  
 
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Brian: So what your saying is that if you were flying an MD80, you would just keep flying along, trimming, retrimming, getting worse and worse, until the plane became uncontrollable and then crash. Yes, Brian, I believe you.

Last edited by TheRobe; 18th Jan 2013 at 21:15.
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Old 19th Jan 2013, 00:31
  #38 (permalink)  
 
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you would just keep flying along, trimming, retrimming, getting worse and worse
You really as thick as a brick son. That is not what happened, and is self evident in what I've posted from the report, if indeed you ever passed english comprehension.
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Old 19th Jan 2013, 01:40
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Let's not have a mud slinging contest gentlemen.

Being a bit of a gear head, I've always wondered whether I would have been able to figure out the likely cause for the jamming trim while inflight.

The proper recovery action for that Air Alaska aircraft, before the nut let go completely, was probably to do a no flap approach into some place with a very long runway-something like Edwards AFB-and to trim the aircraft by moving passengers as necessary. Let the airline figure out how to get it out of there afterwards.

I learned my lesson about malfunctioning flight controls a long while ago. Don't even bother going flying with them if they are not fully functional. They are either completely right, or they are not right at all for flight.

Sea story:
I was assigned a combat air patrol in my F-4 and the pilot who had just flown it told me that there was a little "catch" in the stick in the last bit of nose up stabilator travel and to check it out.
When I did my control checks, by golly, he was right! The last inch of stick travel had an abnormal feel to it, but it moved the full travel. Being gung-ho, I went flying off the ship and returned after an uneventful flight. I downed the aircraft because the stick was supposed to be free for the whole travel. Maintenance needed an aircraft badly for the next launch, so they Upped the aircraft and gave it to the next pilot who also downed it when he felt the slight bind, this time before flying it.

What they found when they investigated the problem made me realize how lucky we had been. An electrical control box for the ARI was mounted on a platform just aft of the stabilizer control rod. The bolts attaching the box to the platform had all fallen out and the box was dangling from its wire bundle on the edge of the platform and contacting the linkage which pushed it out of the way with aft stick causing the "catch". If the box had gone over the edge of the platform, it would have limited how much aft stick was available. Not good when you have to slow down to land aboard an aircraft carrier.

As soon as you are aware of a flight control malfunction that FCOM does not properly address, that is the time to become very defensive and very conservative in your approach. Get it on the ground as safely as possible and let the geniuses figure it out.
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Old 19th Jan 2013, 01:41
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Brian - So you want to rewrite history? So the pilots didn't have any problems, they called dispatch to just talk about the weather and all of a sudden they flopped over into the ocean. Is that about it?

---------------------

Machine - After the death spiral in the ocean, the response by the other Alaska pilots told the tale. You had guys running their trims all the way up...all the way down, full control movements instead of the cursory half ass 'good enough'....

Half the fleet wouldn't take off the next day after a number of pilots found 'discrepancies' in their trim and flight controls. The fleet was grounded and they admit to finding atleast 3 more jackscrews on their way out.

I don't know how many guys took off then landed abruptly after having problems, or thinking they had problems in flight.

Whatever the case, other jackscrew problems existed and once on the radar pilots started taking notice, and hence, no more crashes.

Last edited by TheRobe; 19th Jan 2013 at 01:47.
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