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 | | From: | marc rosen | | Subject: | Off Topic with some relevance (Air turbulence) | | Date: | 22 Jan 2005 17:48:20 -0800 |
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 | This is a sad story and I was amazed thinking about how long-and how
far - the turbulance from a jet could affect a smaller aircraft (Though
not confirmed at this time). Just like dirty wind on a race course but
on a much larger scale. And like the Tsunami, waves are built up by
significant pressures and travel until they are attenuated.
I'm sure some of you aeronautical types can appreciate the effects of
air turbulence better than me.
(I pasted the story below if the link does not work for you. I think
you need to register with the WP to view this article)
Marc
http://www.washingtonpost.com/wp-dyn/articles/A27697-2005Jan21.html
Jet's Presence Noted in Copter Crash
Survivor's Account Raises Wake Turbulence Issue, Report Says
By Michelle Boorstein
Washington Post Staff Writer
Saturday, January 22, 2005; Page B01
A preliminary report on the Jan. 10 medevac helicopter crash near the
Woodrow Wilson Bridge says that a 70-passenger jet passed the area less
than two minutes before the helicopter went down and notes that the
only survivor, a flight nurse, wondered whether it might have left a
wake of dangerous air turbulence.
The nurse, Jonathan Godfrey, 36, of Chesapeake Beach told investigators
for the National Transportation Safety Board soon after the crash that
"we must have hit something," leading to initial speculation that the
helicopter hit one of the construction cranes being used to build a new
bridge.
But the transportation board's report says a traffic surveillance video
shows an aircraft flying over the bridge about the time of the crash
and descending after it had passed above and beyond the cranes being
used to build a new bridge.
The nurse said he called the pilot's attention to the lights on the
cranes, according to the report, "and the pilot acknowledged him." The
report said Godfrey "remembered being over the outer loop of the span
of the bridge, and then being submerged in the water with his seatbelt
on, and his helmet off.
"He stated, 'I don't remember striking something, but my initial
reaction was that we must have hit something.' "
The report does not conclude whether the LifeEvac helicopter -- which
the report described as properly maintained -- encountered wake
turbulence, an invisible whirlwind that comes off a plane's wings, then
sinks and dissipates. The crash killed the other two crew members,
pilot Joseph E. Schaefer III, 56, of Sterling and Nichole Kielar, 29,
of Henrico County.
Wake turbulences can be very powerful and stretch for miles, so much so
that planes are required to travel at certain distances from one
another to avoid them. An Airbus A30-600 that crashed into a Queens,
N.Y., neighborhood in 2001 encountered wake turbulence seconds before
it went down. Airbus said the pilot's use of the rudder after the wake
turbulence caused the tail of the aircraft to come off.
Phone calls to the transportation safety board were not immediately
returned last night.
One air-safety expert said the report did not point to obvious wake
turbulence from the jet, which passed over the bridge 105 seconds
before the helicopter did and which was 900 feet directly overhead.
"Without further study, I would not consider that to be an obvious
danger," said Peter Goelz, former managing director of the
transportation board.
But Todd Curtis, a former Boeing safety official who runs a Web site
about air safety, noted that wake turbulence is more likely to cause
problems when two aircraft are of different sizes. He said it is also
significant that wake turbulence sinks.
"The risk factors are lining up. The question is, how much wake
turbulence was generated by the jet?" he said. "These are the kinds of
conditions that are associated with wake turbulence."
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| | From: | trnsprt at yahoo.com | | Subject: | Re: Off Topic with some relevance (Air turbulence) | | Date: | 23 Jan 2005 19:15:47 -0800 |
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| Bob:
I can't tell if you feel that I was blaming F/O Molin for the crash. I
was not. I worked for the aforementioned airline for 2 years after
they purchased my prior employer... TWA. The corporate and safety
culture were very different there than where I came from. It is my
opinion that your comments are very valid and are reflected in the NTSB
findings. I agree that S. Molin probably received too much of the
blame.
In light of the crash of the Air Evac helo my point was that wake
turbulence is not as much a danger to large transport category aircraft
(airliners), which most people here would be familiar with. Didn't
want anyone to get skittish about flying into Kahalui ;-)
FWIW
Tom
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| | From: | Peter B | | Subject: | Re: Off Topic with some relevance (Air turbulence) | | Date: | Sun, 23 Jan 2005 08:16:22 +0100 |
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"marc rosen" wrote in message
news:1106444900.289906.203460@c13g2000cwb.googlegroups.com...
> This is a sad story and I was amazed thinking about how long-and how
> far - the turbulance from a jet could affect a smaller aircraft (Though
> not confirmed at this time).
One of the theories put forward for the crash of the Tupolev supersonic
transport at the Paris Air Show many years ago was wake turbulence (along
with the usual conspiracy theories), hardly a small craft.
Pete
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| | From: | trnsprt at yahoo.com | | Subject: | Re: Off Topic with some relevance (Air turbulence) | | Date: | 22 Jan 2005 20:58:20 -0800 |
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| Actually I meant First Officer in regard to Sten Molin who was the AA
pilot at the controls of AA 587.
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| | From: | moreforce4 at hotmail.com | | Subject: | Re: Off Topic with some relevance (Air turbulence) | | Date: | 22 Jan 2005 18:39:41 -0800 |
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| A light Cessna with an instructor and student on board were killed at
Vancouver International a couple of years ago when they were given the
go-ahead to take off after a heavy jet. About 2 minutes later, but
enough vortex turbulence that they crashed from about 200 feet.
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| | From: | trnsprt at yahoo.com | | Subject: | Re: Off Topic with some relevance (Air turbulence) | | Date: | 22 Jan 2005 19:33:37 -0800 |
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| In the flying world we call this phenomenon "wake vortices". I can
sorta explain what it is from a stupid Pilot's point of view, which
probably lacks alot compared to the various engineers on this board.
Airflow along a swept wing is not purely forward to back. There is
also a spanwise (from the wing root toward the wingtip) component of
airflow. The air releases from near the tip of the wing in what would
look more like a tornado than what you might imagine. In fact if you
have ever been sitting in a window seat on a aircraft landing or
takeing off in a humid environment you might have noticed the vortice
is "fleshed" out by the combination of cool air and humidity. That
"tornado" or votice has the potential to be very damaging depending on
the configuration of the aircraft creating it. The worst situation is
a heavy aircraft, cleanly configured (no landing gear, flaps or slats)
flying very slowly, ie. a prelanding scenario or post takeoff
scenario. At altitude we do sometimes encounter wake vortices but it
is not nearly as violent as when aircraft are preparing for landing.
Oddly enough once the aircraft initiates lowering the flaps and landing
gear the vortices are minimized.
Not to worry. Generally a transport category aircraft (airliner) has
enough mass and momentum to withstand the worst of wake vortices
created by like sized aircraft. However as evidenced by the crash of
the American Airlines 587 (referenced above) near JFK back in November
2001 the vortices can be severe enough to contribute to a crash even if
they are not the actual causal factor. It is widely accepted that the
Second Officer (co-pilot) responded too aggressively to the wake
turbulence that the flight encountered and aggravated the situation by
full control inputs causing the crash.
http://www.airsafe.com/events/aa587.htm
Now the pisser about wake turbulence is that in my experience it is a
very selective event. The absolute worst wake turbulence I ever
experienced was while flying a medium sized twin engine business
aircraft into Sarasota Fl on a very calm morning. The Aircraft just
ahead of me was similarly sized and generally of a weight not
considered to be a hazard where wake turbulence is concerned. I had
ensured adequate spacing between myself and the aforementioned aircraft
(probably about 90 to 100 seconds). But I'll be damned if their wake
turbulence didn't roll me past 90 degress in close proximity to the
ground. It was a very... ummmm... exciting moment of my life. And
that is what the Ambulance Helo crew had to deal with. They had
probably flown in close proximity to the approach path to Reagan Intl.
on a number of occasions without any previous negative effects. In
fact there is a route that all aircraft must follow when flying the
Potomac so as not to violate the protected airspace near the White
House and associated DC landmarks which would put the one aircraft
almost directly above the other. This was probably a case of being in
the wrong place at the wrong instant.
A real shame. My prayers go out to the families.
Tom
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| | From: | Bob Jacobson | | Subject: | Re: Off Topic with some relevance (Air turbulence) | | Date: | Sun, 23 Jan 2005 20:52:51 GMT |
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| While it is widely accepted that the co-pilot of AA 578 responded
too-aggressively to wake turbulence, it is not so widely accepted that the
crash was a result of pilot error. As a former automatic flight control
technician in the US Air Force, and a sometimes passenger on Airbus
aircraft, I followed the FAA investigation with some interest. I read a lot
of the American Airlines, FAA and Airbus testimony and went over
descriptions and diagrams of the flight control system. Some things
disturbed me about the Airbus systems, and the pilot training program for
the aircraft:
1. In light aircraft the rudder pedals are connected to the rudder with
control cables, and there is direct correlation between rudder pedal travel
and the amount of deflection of the rudder. On large aircraft, especially
fly-by-wire aircraft such as the Airbus, the flight control system changes
the amount of pedal travel and pedal effort with the airspeed. In the
systems I'm familiar with, the flight control system limits rudder
deflection and rate of change of deflection as the airspeed increases. This
is done to prevent overloading of the vertical stabilizer, as loading
increases with airspeed. Pilots have the expectation that the limiting
system will prevent overloading the rudder, and convey this limiting through
the feel of the controls (pedal travel and resistance). It seems in the case
of Airbus this is not true. At the speed of the incident, rather low pedal
effort and deflection can effect large and rapid rudder deflections which
can cause overload.
2. FAA certification of transport aircraft only requires that an airframe
can withstand a single maximum rudder deflection in one direction, followed
by a return to neutral, and Airbus met this standard. However, Airbus knew
that rapid oscillations between full left and full right rudder could cause
structural failure. (Note that in normal air transport flying, pilots have
no reason to rapidly go from full left to full right rudder.)
3. Neither Airbus documentation, nor American Airlines training emphasized 1
and 2 above.
4. The flight data recorder (FDR) on the aircraft recorded filtered data.
That is, it recorded flight data as presented on the pilots instruments,
which has been processed, rather than raw data. Remember, this is a
fly-by-wire system: if the sensor inputs are wrong, or the data is processed
incorrectly, the rudder response could have been greater than the feedback
the system gave the pilot. Without the raw data, the investigators can't be
sure what happened.
5. There have been other accidents in which Airbus aircraft have crashed
where it appears that the flight control system did not react the way the
pilots expected. (Although these incidents did not involve rudder control,
but, I believe, the pitch channel). I believe Airbus had the first
fly-by-wire system for a conventional aircraft (Concorde had the first
fly-by-wire system, but it was a delta-wing supersonic aircraft, and that's
a whole nother story). Although the system seems to have mapped system
response to pilot input well in normal flight conditions, its behavior in
some extreme situations may appear anomalous to pilots.
As a person who has repaired many automatic flight control system failures,
I am not so inclined to rule out system failure or design deficiency, and
look instead for pilot error. As an Airbus passenger I can recall a couple
of flights in which the aircraft was doing low-amplitude Dutch rolls,
indicated to me that the yaw damper was not performing well, and needed
repair or recalibration. (I've never had this experience on a Boeing
aircraft, even though most of my flying has been on Boeing planes.) That's
why this event provoked my interest.
Although the sound-bite summation of the FAA report is "pilot error", a
deeper reading reveals major design/system contributions to the event, as
well as some uncertainty due to the way the flight data was recorded. First
Officer Sten Molin is not here to explain or defend his actions, so it is
all to easy to point at him as the cause of the accident. In the interest of
flight safety, and respect for his survivors, we have look deeper than that.
wrote in message
news:1106451217.957005.20440@z14g2000cwz.googlegroups.com...
> In the flying world we call this phenomenon "wake vortices". I can
> sorta explain what it is from a stupid Pilot's point of view, which
> probably lacks alot compared to the various engineers on this board.
>
> Airflow along a swept wing is not purely forward to back. There is
> also a spanwise (from the wing root toward the wingtip) component of
> airflow. The air releases from near the tip of the wing in what would
> look more like a tornado than what you might imagine. In fact if you
> have ever been sitting in a window seat on a aircraft landing or
> takeing off in a humid environment you might have noticed the vortice
> is "fleshed" out by the combination of cool air and humidity. That
> "tornado" or votice has the potential to be very damaging depending on
> the configuration of the aircraft creating it. The worst situation is
> a heavy aircraft, cleanly configured (no landing gear, flaps or slats)
> flying very slowly, ie. a prelanding scenario or post takeoff
> scenario. At altitude we do sometimes encounter wake vortices but it
> is not nearly as violent as when aircraft are preparing for landing.
> Oddly enough once the aircraft initiates lowering the flaps and landing
> gear the vortices are minimized.
>
> Not to worry. Generally a transport category aircraft (airliner) has
> enough mass and momentum to withstand the worst of wake vortices
> created by like sized aircraft. However as evidenced by the crash of
> the American Airlines 587 (referenced above) near JFK back in November
> 2001 the vortices can be severe enough to contribute to a crash even if
> they are not the actual causal factor. It is widely accepted that the
> Second Officer (co-pilot) responded too aggressively to the wake
> turbulence that the flight encountered and aggravated the situation by
> full control inputs causing the crash.
>
> http://www.airsafe.com/events/aa587.htm
>
> Now the pisser about wake turbulence is that in my experience it is a
> very selective event. The absolute worst wake turbulence I ever
> experienced was while flying a medium sized twin engine business
> aircraft into Sarasota Fl on a very calm morning. The Aircraft just
> ahead of me was similarly sized and generally of a weight not
> considered to be a hazard where wake turbulence is concerned. I had
> ensured adequate spacing between myself and the aforementioned aircraft
> (probably about 90 to 100 seconds). But I'll be damned if their wake
> turbulence didn't roll me past 90 degress in close proximity to the
> ground. It was a very... ummmm... exciting moment of my life. And
> that is what the Ambulance Helo crew had to deal with. They had
> probably flown in close proximity to the approach path to Reagan Intl.
> on a number of occasions without any previous negative effects. In
> fact there is a route that all aircraft must follow when flying the
> Potomac so as not to violate the protected airspace near the White
> House and associated DC landmarks which would put the one aircraft
> almost directly above the other. This was probably a case of being in
> the wrong place at the wrong instant.
> A real shame. My prayers go out to the families.
> Tom
>
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| | From: | Ray Kuntz | | Subject: | Re: Off Topic with some relevance (Air turbulence) | | Date: | Sun, 23 Jan 2005 18:29:15 -0600 |
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| Bob,
Thanks for the very thoughtful analysis.
Ray
Bob Jacobson wrote:
> While it is widely accepted that the co-pilot of AA 578 responded
> too-aggressively to wake turbulence, it is not so widely accepted that the
> crash was a result of pilot error. As a former automatic flight control
> technician in the US Air Force, and a sometimes passenger on Airbus
> aircraft, I followed the FAA investigation with some interest. I read a lot
> of the American Airlines, FAA and Airbus testimony and went over
> descriptions and diagrams of the flight control system. Some things
> disturbed me about the Airbus systems, and the pilot training program for
> the aircraft:
>
> 1. In light aircraft the rudder pedals are connected to the rudder with
> control cables, and there is direct correlation between rudder pedal travel
> and the amount of deflection of the rudder. On large aircraft, especially
> fly-by-wire aircraft such as the Airbus, the flight control system changes
> the amount of pedal travel and pedal effort with the airspeed. In the
> systems I'm familiar with, the flight control system limits rudder
> deflection and rate of change of deflection as the airspeed increases. This
> is done to prevent overloading of the vertical stabilizer, as loading
> increases with airspeed. Pilots have the expectation that the limiting
> system will prevent overloading the rudder, and convey this limiting through
> the feel of the controls (pedal travel and resistance). It seems in the case
> of Airbus this is not true. At the speed of the incident, rather low pedal
> effort and deflection can effect large and rapid rudder deflections which
> can cause overload.
>
> 2. FAA certification of transport aircraft only requires that an airframe
> can withstand a single maximum rudder deflection in one direction, followed
> by a return to neutral, and Airbus met this standard. However, Airbus knew
> that rapid oscillations between full left and full right rudder could cause
> structural failure. (Note that in normal air transport flying, pilots have
> no reason to rapidly go from full left to full right rudder.)
>
> 3. Neither Airbus documentation, nor American Airlines training emphasized 1
> and 2 above.
>
> 4. The flight data recorder (FDR) on the aircraft recorded filtered data.
> That is, it recorded flight data as presented on the pilots instruments,
> which has been processed, rather than raw data. Remember, this is a
> fly-by-wire system: if the sensor inputs are wrong, or the data is processed
> incorrectly, the rudder response could have been greater than the feedback
> the system gave the pilot. Without the raw data, the investigators can't be
> sure what happened.
>
> 5. There have been other accidents in which Airbus aircraft have crashed
> where it appears that the flight control system did not react the way the
> pilots expected. (Although these incidents did not involve rudder control,
> but, I believe, the pitch channel). I believe Airbus had the first
> fly-by-wire system for a conventional aircraft (Concorde had the first
> fly-by-wire system, but it was a delta-wing supersonic aircraft, and that's
> a whole nother story). Although the system seems to have mapped system
> response to pilot input well in normal flight conditions, its behavior in
> some extreme situations may appear anomalous to pilots.
>
> As a person who has repaired many automatic flight control system failures,
> I am not so inclined to rule out system failure or design deficiency, and
> look instead for pilot error. As an Airbus passenger I can recall a couple
> of flights in which the aircraft was doing low-amplitude Dutch rolls,
> indicated to me that the yaw damper was not performing well, and needed
> repair or recalibration. (I've never had this experience on a Boeing
> aircraft, even though most of my flying has been on Boeing planes.) That's
> why this event provoked my interest.
>
> Although the sound-bite summation of the FAA report is "pilot error", a
> deeper reading reveals major design/system contributions to the event, as
> well as some uncertainty due to the way the flight data was recorded. First
> Officer Sten Molin is not here to explain or defend his actions, so it is
> all to easy to point at him as the cause of the accident. In the interest of
> flight safety, and respect for his survivors, we have look deeper than that.
>
>
>
>
> wrote in message
> news:1106451217.957005.20440@z14g2000cwz.googlegroups.com...
>
>>In the flying world we call this phenomenon "wake vortices". I can
>>sorta explain what it is from a stupid Pilot's point of view, which
>>probably lacks alot compared to the various engineers on this board.
>>
>>Airflow along a swept wing is not purely forward to back. There is
>>also a spanwise (from the wing root toward the wingtip) component of
>>airflow. The air releases from near the tip of the wing in what would
>>look more like a tornado than what you might imagine. In fact if you
>>have ever been sitting in a window seat on a aircraft landing or
>>takeing off in a humid environment you might have noticed the vortice
>>is "fleshed" out by the combination of cool air and humidity. That
>>"tornado" or votice has the potential to be very damaging depending on
>>the configuration of the aircraft creating it. The worst situation is
>>a heavy aircraft, cleanly configured (no landing gear, flaps or slats)
>>flying very slowly, ie. a prelanding scenario or post takeoff
>>scenario. At altitude we do sometimes encounter wake vortices but it
>>is not nearly as violent as when aircraft are preparing for landing.
>>Oddly enough once the aircraft initiates lowering the flaps and landing
>>gear the vortices are minimized.
>>
>>Not to worry. Generally a transport category aircraft (airliner) has
>>enough mass and momentum to withstand the worst of wake vortices
>>created by like sized aircraft. However as evidenced by the crash of
>>the American Airlines 587 (referenced above) near JFK back in November
>>2001 the vortices can be severe enough to contribute to a crash even if
>>they are not the actual causal factor. It is widely accepted that the
>>Second Officer (co-pilot) responded too aggressively to the wake
>>turbulence that the flight encountered and aggravated the situation by
>>full control inputs causing the crash.
>>
>>http://www.airsafe.com/events/aa587.htm
>>
>>Now the pisser about wake turbulence is that in my experience it is a
>>very selective event. The absolute worst wake turbulence I ever
>>experienced was while flying a medium sized twin engine business
>>aircraft into Sarasota Fl on a very calm morning. The Aircraft just
>>ahead of me was similarly sized and generally of a weight not
>>considered to be a hazard where wake turbulence is concerned. I had
>>ensured adequate spacing between myself and the aforementioned aircraft
>>(probably about 90 to 100 seconds). But I'll be damned if their wake
>>turbulence didn't roll me past 90 degress in close proximity to the
>>ground. It was a very... ummmm... exciting moment of my life. And
>>that is what the Ambulance Helo crew had to deal with. They had
>>probably flown in close proximity to the approach path to Reagan Intl.
>>on a number of occasions without any previous negative effects. In
>>fact there is a route that all aircraft must follow when flying the
>>Potomac so as not to violate the protected airspace near the White
>>House and associated DC landmarks which would put the one aircraft
>>almost directly above the other. This was probably a case of being in
>>the wrong place at the wrong instant.
>>A real shame. My prayers go out to the families.
>>Tom
>>
>
>
>
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