Talk:Aircraft upset/Archive 1

Rename?

Hello, I would like to kindly suggest we rename this article from "jet upset" to the more general case of "aircraft upset", adding the appropriate redirects and a new section for the specific case of jet upset. You can see some evidence for this change when you Google the following FAA data:

• "jet upset" site:faa.gov currently returns two hits
• "aircraft upset" site:faa.gov currently returns almost 1500 hits.

PolarYukon (talk) 00:51, 31 January 2009 (UTC)

Jet upset

This section needs to be re-written, because the statements are all too often not accurate. Here is how it currently reads:

: Jet upset

A type of aircraft upset is jet upset,[6] although the term has fallen out of favor. The term jet upset was most heavily used in the 1960s and 1970s as the phenomenon was not well understood and still being researched.[7]. Contemporary authors group the phenomenon under loss of control.[8]

Elements of jet upset include:[5]

High altitude wave phenomenon

The aerodynamic effect of mach tuck[9]

Crew inattention[5]

In a jet upset, the aircraft enters rising high altitude wave conditions with autopilot on and full speed trim follow up trimming nose down. Shortly after encountering wave down action, autopilot reaches force limits and disconnects. The crew is behind the aircraft, and the aircraft exceeds critical mach with mach tuck aggravating problem. All jets have altitude/pitch/speed combinations that are unrecoverable.[citation needed] Through the use of drag devices or pitch/power coupling, the aircraft may respond. Control forces become very high and even trimmable stabs may not have ability to increase pitch of aircraft.

===========================

The phrase "jet upset" refers to past accidents (some crashed and some "recovered," with significant damage to the structure), where a jet airliner was "upset" and went into a high dive. That was a phenomena that was almost unknown in the days of piston-driven propeller airliners. That is why they are referred to as "jet" upsets: because it was a repeated phenomena that was unique to jet airliners, with swept-back wings, jet engines and movable horizontal stabilizers, all of which were not found on the piston/propeller airliners.

The first one was a Pan Am 707, that was upset while cruising over the Atlantic at FL 350, on Feb 3, 1959. It did not recover until reaching 6,000 ft. It was landed safely at Gander. Extensive structural damage was incurred, but only a few passengers, plus 10 of the crew, received minor injuries. Of the three elements that are given above, and by implication are alleged to be included in all jet upsets, the safety board cited only one: the inattention of the copilot. There was no mention of mach tuck or a high altitude wave condition, as being causual or contributory to that accident. Indeed, those factors are also not part of many other too, so that part of that section needs to be re-worded.

The second one was NWA, a 720B, that was hit with a powerful updraft as it tried to fly between thunderstorms, right after takeoff. The nose pitched up so high that the pilot used full nose down trim on the HorStab, and the elevators (it was suddenly climbing at 9,000 ft. per minute). Then, an equally powerful down draft hit the plane and it went straight down in a matter of seconds. The pilot, of course pulled back on the yoke, which moved the elevators to the full up position. But, that imposed such a G-load on the plane, that the jackscrew for the HorStab stalled and it remained in the full down position. The plane came apart in the air, before hitting the ground. There was no high-altitude wave condition, nor mach tuck as part of that accident, nor was it blamed on pilot inattention. The plane never made it to cruise altitude. The upset occurred while it was climbing thru 19,000 feet.

On July 12, 1963 Capt. Lynden E. Duesher was in command of United flight 746, a B-720, from San Francisco to Chicago. Near O'Neill, Nebraska, he observed turbulence on his radar. He decided to try and "climb above it," so he began the ascent to 41,000 ft. from his current 35,000 ft. As they passed thru 37,500 ft., they encountered severe turbulence and then downdrafts and then an updraft, causing the plane to approach a stall.

[For the weight and power of that airplane, he was approaching what pilots call "coffin alley," meaning that as the plane climbs, the maximum (mach buffet) speed becomes lower while the minimum (stall) speed becomes higher. The range between those two limiting speeds narrows, until they eventually converge. That becomes the absolute altitude limit of a given plane. Any turbulence produces additional G-force (same as the plane suddenly becoming a lot heavier) and the plane will stall and fall if the speed exceeds either side of that coffin alley envelope.]

The nose pitched up to 15 degrees, and then up to 40 degrees, even though both were pushing full forward on the yoke. The plane stalled and rolled to the left and dove for mother earth. Now the nose was pitched down to 35 degrees. Duesher tried to use the stab trim to help pull the nose up, but it wouldn't work. [I don't know what position the stab trim was in at that time, but apparently not full nosedown, as in the other accidents.] He had pulled the power back to idle and extended the speed brakes. That, plus the fact that he wasn't pointed straight down, kept the plane from exceeding the speed of sound, though it came awfully close. As they approached 15,000 ft. the heavier air enabled them to gingerly apply back pressure on the yoke, while simultaneously increasing engine thrust. They managed to level off at 14,000 ft.

At Chicago, the flight recorder was pulled to examine the actual stresses on the plane. The tracings appeared to be very similar to those found on the FDR of the Northwest 720 crash near Miami (above). Yet, a full examination of the plane revealed no structural damage; not a rivet was popped. The difference, was pilot technique.

After that near disaster, the stall and mach buffet margins were widened on all jet aircraft to preclude a plane getting into that situation again, where severe turbulence narrows the "coffin alley" margins so instantly that the pilots do not have time to avoid a high altitude stall.

On November 29, 1963, a Trans-Canada Airlines DC-8-54F, took off from Dorval Airport, near Montreal. Five minutes later it crashed, leaving a crater in the ground, killing all 118 on board. Impact speed was over 500 mph. They found the horizontal stabilizer trim setting at 1.65 to 2 degrees nosedown and concluded it had moved to that position via hydraulic power (the normal force that moves that stabilizer on the DC-8). They also guessed that the pilot had intentionally trimmed it to that nosedown position -- which was abnormal for a plane taking off. From that, they speculated that the PTC (pitch trim compensator) had malfunctioned and extended too far as the plane's speed accelerated during climb. That would cause the control column to move aft, and the plane to pitch up abnormally. The pilot probably then moved the stab trim to that nose down setting to compensate, causing the plane to suddenly pitch over into a dive.

On February 24, 1964, an Eastern Airlines DC-8 crashed into Lake Pontchartrain about 5 minutes after taking off from the New Orleans Moisant Airport. All 58 on board perished. The water was only 20 ft. deep, yet only 60 % of the wreckage was recovered, because the breakup was so extensive. The FDR tape was too damaged to help the analysis. Instead, they used the maintenance records of that plane, and of other DC-8s, to conclude that the pilots had trimmed the stabilizer to the full nosedown position to counter the excessive noseup attitude that, in turn, was caused by a malfunctioning PTC that had extended too far. Then, when the upset occurred, they could not trim the stabilizer back to the noseup position because the severe forces, generated by their pulling back on the yoke, stalled those jack screws.

There have been many more jet upsets, that did not involve some of the items listed above. I would recommend deleting the citations that lead to Google books, since most of then say little or nothing about the history of actual jet upset accidents. In some cases, all that is there is the highlighted words "jet upset." EditorASC (talk) 10:59, 19 October 2009 (UTC)

I have restored the links to the three accidents in this section. They were not broken. They just require a total of three clicks of the mouse to open tha Official Accident Reports, instead of the usual one click. That is because the DOT website uses .dll links to reach the reports, from the main list of years covered page. Nothing we can do about that. It is just the way they do it at that Govt website.

If you can find a better source for those Official Accident Reports, so that just one click will open the report, then by all means change the link. But, until someone does find a better source for those reports, the existing links should remain. It is better to have citations that do lead to the reports, even if two more clicks are required, than no access at all. I am sure you understand that the actual Official Accident Reports are the best source, so I am mystified as to why you referenced Wiki's policy on reliable sources? They are the best source for airliner accidents. And, they work, with the extra clicks, so do not remove until a better source for those reports can be found. EditorASC (talk) 13:32, 3 December 2009 (UTC)

I removed the latest banner in the jet upset section, simply because it did not match the complaints you have about this section. In other words, that banner was nonsensical. If you think there are problems with this section, then I suggest you spell out those problems on this talk page and give us some idea of how you would improve this section. Just hanging out banners, in hopes of getting other editors to articulate, what you yourself are unwilling to articulate, is not the proper use of banners, and it doesn't help to achieve consensus. EditorASC (talk) 03:28, 9 January 2010 (UTC)

List of Factors

This section is long, tedious and does not provide much in the way of useful information to the average lay reader. I vote for it to be either deleted entirely, or severely modified, if doing that can make it short and informative. EditorASC (talk) 23:45, 19 October 2009 (UTC)

The information is a valuable grouping of factors that are encyclopedic in nature, from a reliable and high-quality source. The information can be moved to a separate article to keep this article short.

PolarYukon (talk) 00:33, 20 October 2009 (UTC)

I don't dispute that the source is high-quality and reliable. However, it is more suitable for a thesis in a professional journal, than it is for this type of Wiki article. If you have an idea of where it should be moved, then I think that would be a good solution. EditorASC (talk) 07:26, 21 October 2009 (UTC)

A page such as List of aircraft upset factors would be suitable. Open to other ideas as well.

PolarYukon (talk) 15:52, 21 October 2009 (UTC)