Paul Wellstone -- King Air Crash
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Paul Wellstone -- King Air Crash
This is a link to a set of articles about the King Air crash that killed Paul Wellstone and some of his family and entourage.
http://www.startribune.com/stories/1752/
If anyone has read the story of 'Dudley' in Fate is the Hunter, then parts of it may seem familiar...
http://www.startribune.com/stories/1752/
If anyone has read the story of 'Dudley' in Fate is the Hunter, then parts of it may seem familiar...
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The NTSB issued a probable cause today. In part, Quote
Washington, DC - The National Transportation Safety Board
today determined that the probable cause of the crash late
last year of a Raytheon (Beechcraft) King Air 100 airplane,
carrying Senator Paul Wellstone and seven others, was the
"flight crew's failure to maintain adequate airspeed, which
led to an aerodynamic stall from which they did not
recover."
Reviewing the results of the extensive investigation into
this accident, NTSB Members concluded that the flight crew
failed to maintain an appropriate course and speed for the
approach to Eveleth and did not properly configure the
airplane at the start of approach procedures.
"During the later stages of the approach," the Board said,
the flight crew "failed to monitor the airplane's airspeed
and allowed it to decrease to a dangerously low level (as
low as about 50 knots below the company's recommended
approach speed) and to remain below the recommended approach
speed for about 50 seconds." The airplane then entered a
stall from which it did not recover.
Washington, DC - The National Transportation Safety Board
today determined that the probable cause of the crash late
last year of a Raytheon (Beechcraft) King Air 100 airplane,
carrying Senator Paul Wellstone and seven others, was the
"flight crew's failure to maintain adequate airspeed, which
led to an aerodynamic stall from which they did not
recover."
Reviewing the results of the extensive investigation into
this accident, NTSB Members concluded that the flight crew
failed to maintain an appropriate course and speed for the
approach to Eveleth and did not properly configure the
airplane at the start of approach procedures.
"During the later stages of the approach," the Board said,
the flight crew "failed to monitor the airplane's airspeed
and allowed it to decrease to a dangerously low level (as
low as about 50 knots below the company's recommended
approach speed) and to remain below the recommended approach
speed for about 50 seconds." The airplane then entered a
stall from which it did not recover.
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An Alternative Explanation - Thoughts??
Excuse the length but this is from an exchange (segregated by the font colors) with someone who doesn’t readily accept automatic pilot error findings (and normally probes for vindication). Looking for some expert opinions here on this theory (most probably from experienced instrument fitters).
From the NTSB PowerPoint
<<<A search of our accident database shows that there have been many general aviation and commercial accidents attributed to inadvertent flight crew failure to maintain airspeed. As this slide shows, there have been 11 Part 135 cases and 7 Part 121 cases since 1982. It is important to note that these 18 commercial cases do not include those attributed to icing conditions, although icing accidents have prompted the Board to recommend higher airspeeds and stall warning thresholds in icing conditions.>>>
EMAILS:
Just to review once again the effect of water trapped/frozen in the static system. The reason for doing so is that an error of up to 50 knots in approach speeds is not something that even the dunciest pilot would do (nor his compadre permit him to). It smells more of instrument error - to me.
Remember that I related to you a personal experience whereby, as I climbed (with a bunch of similar jets) out of XXXXXXXXX back in 1976 we were just about all (5/7 of us) similarly afflicted as we climbed through the freezing level in IMC by trapped water freezing in the lines. Altimeters froze, VSI's froze and airspeed wound back from a 220kt climb to zero in 2700ft (we worked out later) of altitude gain. This is due to the difference between the pressure change trapped in the static lines and the changing static pressure derived from the pitot tube (pitot pressure being static plus dynamic).The Dynamic is the airspeed.
The formula is that indicated (or calibrated/rectified) airspeed = the pitot's pressure (dynamic + static) minus the static port's static pressure (and normally they will be identical plus or minus a few knots due to static port position error). When the latter (i.e. static port's pressure) is stuck at a higher value, eventually in the climb it overcomes the pitot's D+S (this S is reducing as atmospheric pressure drops in the climb) and the indicated airspeed remainder is eventually (after 2700ft of climb at 220kts)= ZERO. That incident was caused by the 5 airplanes being left parked in car-ports during heavy weather and rain running off the fuselage being drawn up the hollow rubber static bungs into the system by capillary action. The solution of course is to bash in the glass face of the VSI, depressurize and use cockpit pressure. We wimped out by doing a radar-directed descent overwater (off the coast) at a very low rate (by shallow attitude selection) until visual below cloud....and the instruments recovered as the lines unfroze.
Now consider a similarly static-line water-afflicted airplane that flies geographically into an area of icing conditions (and suffers the same malady). On descent its indicated airspeed will tend to overread (and so the speed, as measured by radar, will be inordinately low). But as it descends the ice in the lines will melt and perhaps the altimeter/VSI will function normally - or at least appear to correctly indicate a descent (but altimeters may still be errored to a degree). Now will melted-ice water trapped at a low-point in static lines allow the airspeed to recover to normal values during a descent? Not sure about that (how long is a piece of string?) - but perhaps the suction effect would stop the pressure sensed at the ports from being reflected in full at the ASI (think about how you can suck water up a straw and then keep it suspended there. There's a lower air-pressure at your tongue's side of the straw than there is at the open end). It's that lower pressure that causes the overreading ASI.
I just cannot see two individuals sitting there mutually abiding by dangerously low airspeeds - unless that's NOT what they were seeing. I hope that you get it. It may be a viable explanation - seeing as inexplicably low airspeeds on descent/approach is not an unusual situation (according to the NTSB database). It might be a silent killer.
It's important to note that any frozen static-line trapped water in the cruise just wouldn't show up on VSI, ASI or altimeter.
It's a climb and descent phenomena only. In fact if a cruise descent at that same IAS was started, that ice might quickly become water. Once you have water it is free to flow and static pressure changes can be reflected on all three pressure instruments. However the contention, as in the water sucked up a straw principle, is that you do not need a large upstream (of trapped water) low-side differential in order for that airspeed sum to cause an ASI over-reading. Just a few mbs of pressure would do it.
Remember that static lines are only a few mm diameter internally and that capillary action and meniscus formation does mean that although water can travel along such a line, designed-in low drainage points (for water entrapment and drainage) means that there will be some verticality in the lines (i.e. water to be pushed uphill). Therein lies the explanation for altimeter and VSI acting seemingly normally (although with pressure-error induced errors and soggy VSI lags) - but (per the straw analogy) the air between the trapped line-water and the instruments can never totally catch up the pressure increase resulting from the descent from the cruise-level of 13,000ft. Within that pressure discrepancy lies the overreading error (of whatever residual magnitude).
encapsulating these thoughts ==>per below
There is another potential factor that may be worth considering. Why would two pilots allow airspeed to remain slow and then decay to the point of stall without taking action to arrest and reverse the situation? It seems inconceivable that two pilots would mutually abide dangerously low airspeeds, approaching a 50-knot deficit. Maybe that was not what they were seeing. Could instrument error lie at the heart of such pilot passivity? If the aircraft was cold-soaked in the hour's cruise at 13,000 feet, and any water trapped in the static line froze (but later melted on descent), the indicated airspeed would begin to overread during descent and approach (and so the speed, as measured by radar, would be inordinately low). The problem would not show up on the airspeed indicator (ASI) or altimeter during cruise. A tendency for the two cockpit ASIs to read a deceptively high airspeed could result even if the line-trapped ice melted during descent, sources say. Melted-ice water trapped at a low point in static lines seemingly would allow the airspeed to recover to normal (accurate) values during descent and the other pressure instruments (altimeter and VSI) would appear to behave normally . But in a static line just a few millimeters in diameter, capillary action and meniscus formation of water trapped (vertically) in the lines might prevent the pressure sensed at the static ports from being reflected in full at the airspeed indicator.
To illustrate, think about how one can suck water up a straw and then keep it suspended there. There is a lower air-pressure on the tongue's side of the straw than there is at the open end. Per the straw analogy, the air between the trapped line-water and the instruments can never totally catch up to the pressure increase resulting from the descent from the cruise level of 13,000 feet. Within that pressure discrepancy may lie an overreading error (of whatever residual magnitude).Avoiding such problems is why some aircraft static ports are heated and manually operated drains are installed at static line low points.
Because the margin between approach speed and stall speed is oftentimes just a few knots, an accurate airspeed reading is critical. If the airspeed indicator is reading too high, the pilot might fly too slowly and risk stalling - even though content that he's indicating "on speed" . An airspeed indicator overreading 10-15 knots and the slender margin between a stall and any maneuvering for final line-up could be all that's needed to push unsuspecting pilots into a low altitude unrecoverable stall. The NTSB database documents a history of inexplicably low airspeeds on descent and approach. If instrument error is at play here, it is not an unusual situation. It might be a silent killer.
From the NTSB PowerPoint
<<<A search of our accident database shows that there have been many general aviation and commercial accidents attributed to inadvertent flight crew failure to maintain airspeed. As this slide shows, there have been 11 Part 135 cases and 7 Part 121 cases since 1982. It is important to note that these 18 commercial cases do not include those attributed to icing conditions, although icing accidents have prompted the Board to recommend higher airspeeds and stall warning thresholds in icing conditions.>>>
EMAILS:
Just to review once again the effect of water trapped/frozen in the static system. The reason for doing so is that an error of up to 50 knots in approach speeds is not something that even the dunciest pilot would do (nor his compadre permit him to). It smells more of instrument error - to me.
Remember that I related to you a personal experience whereby, as I climbed (with a bunch of similar jets) out of XXXXXXXXX back in 1976 we were just about all (5/7 of us) similarly afflicted as we climbed through the freezing level in IMC by trapped water freezing in the lines. Altimeters froze, VSI's froze and airspeed wound back from a 220kt climb to zero in 2700ft (we worked out later) of altitude gain. This is due to the difference between the pressure change trapped in the static lines and the changing static pressure derived from the pitot tube (pitot pressure being static plus dynamic).The Dynamic is the airspeed.
The formula is that indicated (or calibrated/rectified) airspeed = the pitot's pressure (dynamic + static) minus the static port's static pressure (and normally they will be identical plus or minus a few knots due to static port position error). When the latter (i.e. static port's pressure) is stuck at a higher value, eventually in the climb it overcomes the pitot's D+S (this S is reducing as atmospheric pressure drops in the climb) and the indicated airspeed remainder is eventually (after 2700ft of climb at 220kts)= ZERO. That incident was caused by the 5 airplanes being left parked in car-ports during heavy weather and rain running off the fuselage being drawn up the hollow rubber static bungs into the system by capillary action. The solution of course is to bash in the glass face of the VSI, depressurize and use cockpit pressure. We wimped out by doing a radar-directed descent overwater (off the coast) at a very low rate (by shallow attitude selection) until visual below cloud....and the instruments recovered as the lines unfroze.
Now consider a similarly static-line water-afflicted airplane that flies geographically into an area of icing conditions (and suffers the same malady). On descent its indicated airspeed will tend to overread (and so the speed, as measured by radar, will be inordinately low). But as it descends the ice in the lines will melt and perhaps the altimeter/VSI will function normally - or at least appear to correctly indicate a descent (but altimeters may still be errored to a degree). Now will melted-ice water trapped at a low-point in static lines allow the airspeed to recover to normal values during a descent? Not sure about that (how long is a piece of string?) - but perhaps the suction effect would stop the pressure sensed at the ports from being reflected in full at the ASI (think about how you can suck water up a straw and then keep it suspended there. There's a lower air-pressure at your tongue's side of the straw than there is at the open end). It's that lower pressure that causes the overreading ASI.
I just cannot see two individuals sitting there mutually abiding by dangerously low airspeeds - unless that's NOT what they were seeing. I hope that you get it. It may be a viable explanation - seeing as inexplicably low airspeeds on descent/approach is not an unusual situation (according to the NTSB database). It might be a silent killer.
It's important to note that any frozen static-line trapped water in the cruise just wouldn't show up on VSI, ASI or altimeter.
It's a climb and descent phenomena only. In fact if a cruise descent at that same IAS was started, that ice might quickly become water. Once you have water it is free to flow and static pressure changes can be reflected on all three pressure instruments. However the contention, as in the water sucked up a straw principle, is that you do not need a large upstream (of trapped water) low-side differential in order for that airspeed sum to cause an ASI over-reading. Just a few mbs of pressure would do it.
Remember that static lines are only a few mm diameter internally and that capillary action and meniscus formation does mean that although water can travel along such a line, designed-in low drainage points (for water entrapment and drainage) means that there will be some verticality in the lines (i.e. water to be pushed uphill). Therein lies the explanation for altimeter and VSI acting seemingly normally (although with pressure-error induced errors and soggy VSI lags) - but (per the straw analogy) the air between the trapped line-water and the instruments can never totally catch up the pressure increase resulting from the descent from the cruise-level of 13,000ft. Within that pressure discrepancy lies the overreading error (of whatever residual magnitude).
encapsulating these thoughts ==>per below
There is another potential factor that may be worth considering. Why would two pilots allow airspeed to remain slow and then decay to the point of stall without taking action to arrest and reverse the situation? It seems inconceivable that two pilots would mutually abide dangerously low airspeeds, approaching a 50-knot deficit. Maybe that was not what they were seeing. Could instrument error lie at the heart of such pilot passivity? If the aircraft was cold-soaked in the hour's cruise at 13,000 feet, and any water trapped in the static line froze (but later melted on descent), the indicated airspeed would begin to overread during descent and approach (and so the speed, as measured by radar, would be inordinately low). The problem would not show up on the airspeed indicator (ASI) or altimeter during cruise. A tendency for the two cockpit ASIs to read a deceptively high airspeed could result even if the line-trapped ice melted during descent, sources say. Melted-ice water trapped at a low point in static lines seemingly would allow the airspeed to recover to normal (accurate) values during descent and the other pressure instruments (altimeter and VSI) would appear to behave normally . But in a static line just a few millimeters in diameter, capillary action and meniscus formation of water trapped (vertically) in the lines might prevent the pressure sensed at the static ports from being reflected in full at the airspeed indicator.
To illustrate, think about how one can suck water up a straw and then keep it suspended there. There is a lower air-pressure on the tongue's side of the straw than there is at the open end. Per the straw analogy, the air between the trapped line-water and the instruments can never totally catch up to the pressure increase resulting from the descent from the cruise level of 13,000 feet. Within that pressure discrepancy may lie an overreading error (of whatever residual magnitude).Avoiding such problems is why some aircraft static ports are heated and manually operated drains are installed at static line low points.
Because the margin between approach speed and stall speed is oftentimes just a few knots, an accurate airspeed reading is critical. If the airspeed indicator is reading too high, the pilot might fly too slowly and risk stalling - even though content that he's indicating "on speed" . An airspeed indicator overreading 10-15 knots and the slender margin between a stall and any maneuvering for final line-up could be all that's needed to push unsuspecting pilots into a low altitude unrecoverable stall. The NTSB database documents a history of inexplicably low airspeeds on descent and approach. If instrument error is at play here, it is not an unusual situation. It might be a silent killer.
