LJ45
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- Jan 2, 2005
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"National Transportation Safety Board member Debbie Hersman said a cockpit voice recording of the Friday night crash indicates the crew tried to abort the takeoff, but then signaled the efforts were failing.
"The crew reacted to a sound that was consistent with a tire blowout," Hersman said.
Hersman said no cause of the crash has been determined and the investigation is ongoing. She did say that pieces of tire were recovered about 2,800 feet from where the plane started its takeoff. The runway is 8,600 feet long. The plane was traveling at least 92 mph, its minimum takeoff speed, when the crew thought the tire burst, Hersman said."
And this if from the Learjet 60 accident at Troy, AL:
With an estimated empty weight of 15,800 pounds and estimated fuel of 1,100 pounds, it was calculated that the airplane traveled 1500 feet down the runway after touchdown in 4.2 seconds before striking the deer, the performance group at Learjet using the weather reported at Troy, Alabama (variable winds and temperature at 14 degrees Celsius) the airplane landed with a ground speed of 124 knots. At 124 knots and maximum braking applied, the airplane should have come to a complete stop in about 850 feet.
A sound spectrum study was conducted using the Cockpit Voice Recorder as the source of the sound. The study was conducted by the National Transportation Safety Board's Vehicle Recorders Division. The study revealed that the engines fan speed increased from 8727.5 (82.3 percent) rpm to 9590 (90.4 percent) rpm between 11 seconds after touchdown and 18.2 seconds after touchdown. This increase in fan speed does not achieve the calculated takeoff N1, however, this engine speed is higher than achievable on a reverse thrust schedule. According to Pratt and Whitney of Canada, N1 is governed during reverse operations. The governing limit varies, and is based on ambient conditions and the airspeed. At 100 knots or greater, the maximum governing limit for N1 should be about 85.2 percent (according to Bombardier Aerospace) instead of the 90 percent found on the engines 20.4 seconds after landing.
Normal operating procedures include deploying the thrust reversers within 4 to 6 seconds after landing. Pilots deploy thrust reversers (T/R) by raising piggyback levers located in the cockpit with the throttles. With the loss of the squat switch on the left main landing gear, the T/R relay box deenergized the deploy solenoid and the T/R's go to the stow position. The electronic engine control (EEC) commands the engine speed to go to idle. As the T/R's complete the stow cycle, the unlock switches open, signaling the T/R relay box to remove the discrete signals. The EEC's switch to the forward thrust schedule and within 2.6 seconds estimated, and if the piggybacks remain at the max reverse position the engines rpm begins to increase to near takeoff power.
full report http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20010119X00328&ntsbno=ATL01FA021&akey=1
"The crew reacted to a sound that was consistent with a tire blowout," Hersman said.
Hersman said no cause of the crash has been determined and the investigation is ongoing. She did say that pieces of tire were recovered about 2,800 feet from where the plane started its takeoff. The runway is 8,600 feet long. The plane was traveling at least 92 mph, its minimum takeoff speed, when the crew thought the tire burst, Hersman said."
And this if from the Learjet 60 accident at Troy, AL:
With an estimated empty weight of 15,800 pounds and estimated fuel of 1,100 pounds, it was calculated that the airplane traveled 1500 feet down the runway after touchdown in 4.2 seconds before striking the deer, the performance group at Learjet using the weather reported at Troy, Alabama (variable winds and temperature at 14 degrees Celsius) the airplane landed with a ground speed of 124 knots. At 124 knots and maximum braking applied, the airplane should have come to a complete stop in about 850 feet.
A sound spectrum study was conducted using the Cockpit Voice Recorder as the source of the sound. The study was conducted by the National Transportation Safety Board's Vehicle Recorders Division. The study revealed that the engines fan speed increased from 8727.5 (82.3 percent) rpm to 9590 (90.4 percent) rpm between 11 seconds after touchdown and 18.2 seconds after touchdown. This increase in fan speed does not achieve the calculated takeoff N1, however, this engine speed is higher than achievable on a reverse thrust schedule. According to Pratt and Whitney of Canada, N1 is governed during reverse operations. The governing limit varies, and is based on ambient conditions and the airspeed. At 100 knots or greater, the maximum governing limit for N1 should be about 85.2 percent (according to Bombardier Aerospace) instead of the 90 percent found on the engines 20.4 seconds after landing.
Normal operating procedures include deploying the thrust reversers within 4 to 6 seconds after landing. Pilots deploy thrust reversers (T/R) by raising piggyback levers located in the cockpit with the throttles. With the loss of the squat switch on the left main landing gear, the T/R relay box deenergized the deploy solenoid and the T/R's go to the stow position. The electronic engine control (EEC) commands the engine speed to go to idle. As the T/R's complete the stow cycle, the unlock switches open, signaling the T/R relay box to remove the discrete signals. The EEC's switch to the forward thrust schedule and within 2.6 seconds estimated, and if the piggybacks remain at the max reverse position the engines rpm begins to increase to near takeoff power.
full report http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20010119X00328&ntsbno=ATL01FA021&akey=1
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