Air Midwest 5481

[Timebuilder]

NTSB CITES MECHANIC'S ERROR IN CHARLOTTE CRASH
A combination of an overweight condition, aft center of gravity and improperly set elevator control cables are to blame for the crash of a US Airways Express Air Midwest Flight 5481. This was the official probable cause reached by the NTSB at its recent public meeting on May 20-21. You may remember AVweb's initial coverage of the Beech 1900D, which crashed at Charlotte-Douglas International Airport on Jan. 8. Investigators determined that while the weight-and-balance issues were factors, they think the turboprop might have made the flight to the Greenville-Spartanburg Airport in South Carolina anyway had it not been for a mechanic's mistake two nights before the deadly crash.

http://www.avweb.com/newswire/9_22b/complete/185073-1.html#3b

 

[enigma]

Quoted from the Avweb article. "A combination of an overweight condition, aft center of gravity and improperly set elevator control cables are to blame for the crash of a US Airways Express Air Midwest Flight 5481. This was the official probable cause reached by the NTSB at its recent public meeting on May 20-21. You may remember AVweb's initial coverage of the Beech 1900D, which crashed at Charlotte-Douglas International Airport on Jan. 8. Investigators determined that while the weight-and-balance issues were factors, they think the turboprop might have made the flight to the Greenville-Spartanburg Airport in South Carolina anyway had it not been for a mechanic's mistake two nights before the deadly crash. Investigators determined that when the elevator cables' tension were set, the control column was set too far forward, meaning the control column could be pushed forward only a slight distance before hitting its stops. Officials revealed in their report that a trainee mechanic admitted skipping several steps in the maintenance manual detailing cable tension adjustments, as he felt they were unnecessary. Initial reports that the plane might be overweight prompted the FAA to order a survey of average passenger weights, discovering that passengers today weigh an average of almost 21 pounds more than in 1995 at the time of the last survey, and they are carrying heavier luggage. As a result the agency has ordered an increase in the average weights used in calculating aircraft weight and balance.



What kind of control check does Mesa accomplish on the 1900? I flew the mighty Beech at Mesa, but have not sat in one since 1992 and don't remember the check. I assume that the preflight/after start/taxi/before takeoff checks would include a control freedom check. This would appear to be a good reminder that NOTHING is on the checklist without a reason.

regards,
enigma

 

[A Squared]

Enigma,


>>>>>>What kind of control check does Mesa accomplish on the 1900? I flew the mighty Beech at Mesa, but have not sat in one since 1992 and don't remember the check. I assume that the preflight/after start/taxi/before takeoff checks would include a control freedom check.

My understanding is that the control column would go all the to the control column's normal forward stop, but with the control column all the way forward, the elevator was at a fraction of its full down deflection.

I suppose that begs the question ... would that then prevent the control column from reaching it's full aft travel? I don't know.

regards

 

[enigma]

AA, I do want to give the crew the benefit of the doubt, but the wording of the NTSB statement that I cut and pasted, definitely says that the controls could only be pushed forward a small amount before they reached the stops. In time we will get this statement clarified; I pray that you are reading it correctly and my interpretation is incorrect.

You have an excellent point about the aft travel. Something still doesn't make sense here.

regards,
8N

 

[flx757]

NTSB CITES MECHANIC'S ERROR IN CHARLOTTE CRASH
A combination of an overweight condition, aft center of gravity and improperly set elevator control cables are to blame for the crash of a US Airways Express Air Midwest Flight 5481. This was the official probable cause reached by the NTSB at its recent public meeting on May 20-21.

http://www.avweb.com/newswire/9_22b/complete/185073-1.html#3b

This is an extremely misleading, if not out-and-out false statement. This investigation is ongoing . The NTSB has not determined the probable cause, and no final report has been issued. All the current public information on this accident is available on the NTSB website, including the public docket which contains the various group chairmen's reports. The following is a direct quote taken from the opening statement made by Ellen Engleman, Chairman of the NTSB at the beginning of the public hearings of May 20 & 21, which the Avweb article references. Note that she makes a point of stating that no probable cause will be determined at the hearings. It bears repeating that this investigation is ongoing. For Avweb to state that a probable cause has been determined is very irresponsible. Here is the excerpt from Chairman Engleman's statement: (I added the italics were added for emphasis)

The hearing is being held for the purpose of supplementing the facts, conditions, and circumstances discovered during the on-scene and continuing investigation. This process will assist the Safety Board in determining the probable cause of the accident and in making any recommendations to prevent similar accidents in the future. No determination of cause will be rendered during these proceedings.


One interesting detail that I gleaned from the various group chairman reports, and it, in a way, relates to the discussion above about the control column, was that the accident aircraft was flown 9 times prior to the accident flight (flt 5481 was the 10th) since the repairs to the elevator were made. The same crew that flew this flight had flown 6 of those 9 flights. If there really were some noticeable anomally with the elevators, one that would be readily identifiable under normal conditions, it would seem to me that it would have been apparent to this crew.

 

[metrodriver]

There are 2 sets of stops on the controls. At the elevators are a up limit and a downlimit stop, and at the yoke is a forward/rearward limit. The way it normally works is that when you move the yoke the limit stops at the elevator should be reached first. When you pull back on the yoke you feel almost all the way aft the stop (on the elevator), and you can pull back on the yoke a little more stretching the cables. If the yoke is all the way forward you should be able to push the yoke a little bit further against the cable tension. If at anytime the yoke hits the yoke stops, your elevators do not reach full travel. This is one important part of your control check, especially since you don't see much of the elevators in a lot of planes.
I personally found this out in a c182, where the plane landed nosewheel first with the yoke all the way back against the stop. After my complaining a mechanic told me to hold the yoke all the way back and he was able to push the elevator one more inch up before it reached its stop. On the metro the forward (down stop is important, since too much slack in the cable can result in the yoke leaning against the HSI glass, or even breaking through it under gusty condition or releasing the yoke on the ground

 

[A Squared]

Enigma,

My comments are based on having read the technical information released by teh NTSB on the FDR data and the examination of the control system.

I had never seen the statement you reference, and in reading it and the Avweb article, I believe that it is not the NTSB's statement but rather the words of one of Avweb's writers. The information from the NTSB investigation does not seem to support the statement in the Avweb article.

The Flight Data Recorder data shows that on each of the previous 9 flights, which followed the Maintenance, the position of the control column was 10 degrees further forward during cruise that it normally would be. I don’t think that the 1900 has a trimmable horizontal stabilizer, so the assumption is that the elevator would have to be in the normal cruise position, otherwise the airplane would be descending.

The report on the examination of the flight controls stated that the turnbuckle on the down elevator cable was abnormally extended, and that the turnbuckle on the up elevator cable was screwed down to an abnormally shortened position. Now think about it, if the cable that pulls the elevator down is too long and the cable that pulls it up is too short, how does that affect the position of the elevator relative to the position of control column? Right, it means less than full down elevator deflection with a full forward position of the control column. This is independently confirmed by the FDR data. In fact the FDR data suggests that they would get 10 degrees less deflection with the control column at the forward stop. It should be noted that normal full down elevator deflection in the Beech 1900 is 14 degrees, so a loss of 10 degrees is pretty significant As far as I can see there would be no abnormal limit to forward control column travel. Now, it might result in less than normal control travel *back*, but I’ve noticed that a lot of pilots don’t check for full aft travel. I do, and it seems to annoy some of the chubbier captains I fly with.

It would appear that whoever wrote the Avweb article really didn’t understand the information that the NTSB has released. Is it just me, or has the quality of Avweb decreased noticeably since it was purchased?

regards

 

[enigma]

AA, thanks. If they had only four degrees of down elevator as the numbers seem to indicate, it would seem to me that the situation would have manifested itself on an earlier flight. I could see a four degree travel loss just lurking until the time was right/wrong, but the ten degree loss has me wondering.

regards,
8N

 

[metrodriver]

That would not be the case if all previous flights were lightly loaded. Remember on this flight they had a full load of 19 pax and their bags. The metro's I flew would sometimes have an average of 3 people on board and then suddenly you had 19 and a baggage load that could support a Mount Everest expedition for 2 month, all to go to the beach for a few days. Now on takeoff you will need all the nosedown force your elevators can create. (and hopefully some mechanic had adjusted them long ago to the correct settings)

 

[jetdriven]

the 1900 has a very wide CG range for its size. normal GC empty or lightly loaded would be far forward of the aft limit of 40% of MAC.
the yoke rests against its forward stop. a control check is performed in a "box" pattern and it was done. just the elevator only went down 4 degrees and up a lot more than it should.

the aircraft ws legal with the weight and balance. according to the FAA and AMW, the estimated bag weights and passenger weights put the aircraft in the cg -weight envelope.

it was maintenance. easier to blame fallen pilots, though...