Page:NTSB RAR-92 01.pdf/28

 how an end-of-tape mark could have appeared on the accident magnetic tape. The data pack could have been opened, the tape spool lifted up and away from the ratchet mechanism, the tape wound in the direction of the most recently recorded data, and the end-of-tape mark placed on the tape. Or, the initial readout could have been made without an end-of-tape mark and the data pack could have been pulled out of the readout machine just before Route 128 (MP 217.3) data. Amtrak officials stated that they do not believe either action was ever taken.

Because an end-of-tape mark prevents a strip chart output of data, laboratory engineers extracted the data manually. During the initial readout generated on the laboratory's Pulse readout machine, they had copied the data to 1/4-inch magnetic tape, reel-to-reel. Using the reel-to-reel copy, they performed subsequent readouts and evaluations. They extracted the remaining raw data from the end-of-tape mark area and converted it to engineering units. The conversions yielded information on speed, distance travelled, and brake and throttle positions. Since recorded elapsed time data were not recoverable, they derived the elapsed time from the known timing on the event recorder data.

The recovered Pulse event recorder data indicate that from the last stop at Route 128, Amtrak train 66 accelerated at throttle run 8 position with brakes released to a maximum speed of 109 mph, which was achieved approximately 5,400 feet before the last recorded data at MP 227.45. A single full-service brake pressure reduction of 32 psi was recorded, it occurred 4,940 to 4,024 feet before the last recorded data. A single throttle position change from maximum run 8 position to idle was recorded 4,024 to 3,127 feet before the last recorded data. Brake pressure and throttle position values remained constant throughout the remaining recorded data. The last recorded speed was 76 mph, and no emergency brake application was recorded that would indicate that the pneumatic control switch (PCS) was open. When the PCS has been opened by an emergency brake application, the Pulse event recorder senses it electronically. The brake and throttle data are sampled and recorded about every 5 3/4 seconds. Therefore, if the PCS was opened within the last 5 3/4 seconds, the emergency brakes may have been set and not recorded. (For event recorder data recovered from Amtrak train 66, see figure 8.)

—On December 21, 1990, a Safety Board investigation team conducted stopping distance tests between Kingston (MP 158.1) and Davisville (MP 168.3) using a train consist similar to that of Amtrak train 66 on the date of the accident. The test train carried no passengers. To simulate the stopping distance, the investigators used information recovered from the Pulse event recorder and provided during witness testimony. When stopping the train from speeds of 103 to 108 mph, the automatic airbrakes, with the independent brake released, were applied 4,950 to 4,400 feet before a mark that indicated the POD. Test results showed that Amtrak train 66 would have been moving 76 to 80 mph at the POD.