The Four Missing Seconds Analysis from the
26 September, 2000
Condensed Version of the 4 Missing Seconds
Analysis, TWA FL 800 FDR Tape
When the TWA FL 800 43 data word subframes were blocked into 64 word record blocks a repetitive and orderly set of word group patterns were generated within each record block. This blocking, necessary to support the burst-recording and Checkstroke FDR functions, produced 43 different 64 word block groups each with a unique set of words. Of these 43 unique word block groups only one block starts with subframe word 1, only 1 block starts with subframe word no. 2, etc. Also, only one block ends with subframe word no.1, only one block ends with subframe word no. 2, etc.
The NTSB published their Tabular Data in a format, which preserved the record block groups, separated usually by horizontal lines in their Data Tables. Although the NTSB did not publish the entire 43 word subframe contents recovered from the 64 word record blocks of FL 800 they did publish a significant number of flight parameter words. This enabled analysts to easily identify the unique word block group associated with each record block entry in the NTSB Tables.
By arbitrarily defining the unique record block, which starts with subframe word no. 1 as Superframe Block no. 1, we find the last NTSB entry block in their FL 800 Tabular Data Charts No.1 and No. 2 is Superframe data block no. 31. Therefore, the implication is the end of the FDR data stream occurred at the end of data block 31 in the 17th and last Superframe of FL 800 data.
But NTSB Addendum No. 2, Fig. 3, shows a different endpoint of the FDR tape. This Fig., an actual pictorial of the waveforms found at the very end of the FL 800 tape, is annotated with the following "Bits 1-9 of Word 4". This last word 4 was followed by an 8 bit postamble thereby verifying that word 4 was the last word in the last FL 800 record block. But, only one unique record block ends in subframe word 4, and it's block 35, not block no. 31!
Accordingly, waveforms for data record blocks 32, 33, 34 and 35 exist pictorially at the end of the FL 800 FDR tape but their flight parameter values have been withheld from the public dockets by the FBI/NTSB.
The flight parameter values in these last 3,000 bits of the FDR data stream, particularly the vertical and longitudinal accelerations, may well hold the answer as to what happened in these last four seconds of FL 800 to cause it's disintegration at 13,700 feet.
Note: The terms "data record block", "data block", "record block" and
Background for the 4 Missing Seconds Analysis for the TWA Flight 800 FDR Tape
The TWA FL 800 Flight Data Recorder, FDR, tape-recorded a very
unique frame of flight parameter data. One DATA SUBFRAME contains 43 twelve-bit
words, allocated over 18 flight performance categories and 10 documentation
or "housekeeping" parameters.
The TWA FL 800 FDR "burst-mode" recorded the 43 word data subframes after they were serially assembled into DATA RECORD BLOCKS, each record block comprising 64 twelve-bit words. The FDR recorded these data blocks at the average rate of one block per second, but at a burst rate writing speed over 11,000 bits per second at 5-ips tape speed.
A Checkstroke QC feature of the FDR provided for stopping and rewinding the tape after the recording of each one-second data block. During rewind, the last data block just written was read back and it's contents verified. Subsequent data blocks were then recorded after insertion of small inter-record blank gaps on the tape.
Before recording, all 12 bit-word formatting was organized into a single serial bit stream, which was recorded onto the active single tape track of an 8-track 1/4-inch wide tape. The serial bit stream record blocks contained 12 X 64 or 768 data bits per block, at a one block per second rate. See NTSB Exhibit 2.
In addition to the 768 data bits each record block contained a directionally symmetrical set of pre- and postambles, each containing 8 bits, i.e. 0000 0001 (64 data words) 1000 0000. These fixed 8 bit words were electronically attached/spliced to the beginning and end of each data block, before recording, for ease of establishing playback data block boundaries.
Playback processing and publishing of the FDR data by the NTSB was accomplished in unique and orderly one-second data block groupings. In each published one-second data block, 64/43 data subframes were included, i.e. about 1 1/2 data subframes for each data block grouping. For ease of reading, the NTSB published only selected flight parameters, with no documentation parameters, in the one-second data block groupings. See NTSB Exhibits 3A and 3B.
The FDR tape contains no time track per se. However, GMT months, days, hours, minutes and seconds are embedded in the FDR data frame as documentation words 4 through 8. Although the FL 800 GMT words were never decoded and published by the NTSB they were found to be cyclically and properly incrementing by citizen inspection of Freedom Of Information Act FDR waveform sets. The NTSB reluctantly and belatedly released this FOIA data. (Ref. 1)
The NTSB time tagged each of their published one-second data block flight
parameter groups with a time-of-flight in hours, minutes and seconds derived
from NTSB microphone keying event comparisons with the CVR transcript.
The CVR tape contained no time track per se and CVR transcript time was
established by NTSB speech event comparisons with the Boston Air Traffic
Control Tower Tape. The ATC tower tape does contain an "E code" time
track containing Julian days, hours, minutes and seconds.
FL 800 FDR PCM and Tape Format Synopsis
Channel Code: Bi-phase mark
Average record data bit rate: 43 X 64 bps, one record block per second
1, Parameter List, p. 9, FDRFR Rev. 1, Feb. 15, 2000
TWA Flight 800 Data Word Playback Location Patterns
The playback 43 word DATA SUBFRAMES, when serially assembled and blocked into 64 word RECORD BLOCKS, produce unique word pattern groups on playback. These unique patterns are lost if the playback processing is "seamless" with time, i.e. the pre- and post-ambles are discarded and the one-second record blocks are rejoined/spliced perfectly together with the inter-record playback time gaps removed. The playback processing preserves the data word inventory and word group patterns only when the data words are presented in one second, stand alone groups of the recovered record blocks.
The NTSB Flight Parameter Tabular Data No. 1, Revised 15 Feb., 2000, does present the processed flight parameter data words preserved in the one-second groups or record blocks in which they were burst recorded. This enables the playback word group patterns to be used as a potential embedded elapsed time measurement tool.
This potential is confirmed by inspection of NTSB Exhibit 3A, which shows a unique pattern in the lower page right side for data words 34, 35, 36 and 37, the 4 Engine Pressure Ratios. After appearing in preceding one-second data blocks in a clear and repeatable inventory pattern of 1, 2, 1, 2 , 1, 2-- the pattern is uniquely altered to 1, 2, 1, 2, 1, 1, 2, 1, 2 --. Moreover the unique "1, 1 " inventory pattern can be seen to move sequentially and orderly in time from word 37, to 36, to 35, to 34, in perfect descending order of word number sequence. See highlighted words in NTSB Exhibit 3A.
Inspection of the Tabular Data No. 1 contents precisely 43 data blocks earlier shows an exact duplication of the unique 1, 1 appearance pattern for words 34, 35, 36 and 37. This discovery indicates that the data word playback location patterns have a 43 record block and 43 second periodicity. See NTSB Exhibit 4A & 4B, ( highlighted words).
These discoveries led to the construction of a FL 800 SUPERFRAME Matrix showing the detailed appearance patterns of the 43 data subframe words in the 64 word data record blocks. See GS Exhibit - 1.
This SUPERFRAME Matrix was "synchronized" or reset to a convenient start pattern by initially allowing data subframe word 1 to start in record block word 1 position. This synchronization allows the individual one-second data record blocks to be sequentially numbered from to 1 to 43. At sequential block position 44, data subframe word 1 will reappear in word 1 of the one-second data record block, starting Superframe No. 2, etc.
This SUPERFRAME Matrix was then used as a check or inspection tool to see if the NTSB Tabular Data No. 1 of flight parameter word grouping patterns on playback conformed to the constructed Matrix. The word pattern groups matched perfectly.
The Various Versions of the Final One-Second Data Block from TWA Flight 800.
The initial version of the processed FDR tape Flight Parameter Tabular
Data No.1 ended with the last one-second data record block grouping containing
an expectedly aberrant set of flight parameter engineering values. This
expectation was based on the lead FBI investigator announcing early on
that both black box tapes ended with "not normal" signal contents.
Shortly after publication of Exhibit 5 in Dec., 1997, parameter Tabular Data No. 1 was revised and the last one-second data record block, still legible, was lined through the center with a note "End of FL 800 Data". See NTSB Exhibit 6, (highlighted words).
The NTSB later explained this redactive editing as resulting from their inadvertently processing the FDR tape as if the FL 800 data had not stopped at the leading edge of the three-inch erase gap. This failure to stop the processing at the end of the last valid data record block before the erasure gap resulted in data from FL 803, recorded 25 tape-hours earlier, being blended with the last data from FL 800. The NTSB mistake in publishing the unsynchronized FL 803 data, as if it were the last "not normal" data from FL 800, accounted for producing the anomalous values in what was originally published as the last one-second data record block from FL 800, Ref. CVR Time 20:31:12.
The NTSB later made the elimination of the last 800/803 blended data record block from the Parameter Tabular Data No. 1 table complete by total redaction of this anomalous data block. See NTSB Exhibit 7, (highlighted area).
The last complete one-second data record block in Exhibit 7 then showed a set of flight parameter engineering values totally in agreement with the immediate predecessor blocks of flight data, i.e. no anomalous or aberrant values. Also, this block contains a unique and expected word group pattern consistent with it's immediate predecessor data record blocks, i.e. no evidence was found of time or data record block sequence discontinuities. This fact was established using the data record block playback word group patterns as an embedded elapsed time measurement tool.
Accordingly, using the most current NTSB Tabular Data No. 1, the last valid and legible one-second data record block word pattern from FL 800 clearly matched the 31st sequential data block word pattern in Superframe 17! See GS Exhibit -2, (highlighted).
The last word in data block 31 is always data word 6., i.e. GMT hours!
5, p. 42, Tabular Data No. 1,Created Jan. 09, 1997; Report Feb. 28,
Firmly Establishing the Last TWA FL 800 Data
Record Block as Block 31 of Superframe 17
Rigorous proof is required to support the stated goal of this section
of the analysis.
The fact that flight parameter data words do not always appear an equal number of times, from data block-to-data block, provides a recognizable change in pattern useful for data block aligning/synchronizing the NTSB Tabular Data with the GS -1 Matrix. The following analysis steps will illustrate the use of the "unique word inventory pattern" analysis tool, as well as providing the necessary rigor for the "Block 31 of Superframe 17" statement of above.
The data block-to-data block inventory of word patterns for Flight Parameter
Words 37, 36, 35 and 34 provides a good index point to start an analysis.
The unique appearance pattern of these four words establishes a contiguous
8 data block segment that can be easily located both in the NTSB Flight
Parameter Tabular Data No.1, and in the Superframe GS Matrix. Joint inspection
of NTSB Exhibits
3A and 3B,
and GS -1 reveals
the following matching word patterns:
Note: The above 8-block unique inventory pattern is found to be identically present in both the Superframe Matrix and in the NTSB Flight parameter Tabular Data No. 1. This permits data block alignment synchronization of the NTSB Tabular Data No.1 with the Superframe Matrix.
As a confidence establishing self-check we match patterns of two supercommutated flight parameters each using three data word sets per data subframe, the Vert. and Long. Acceleration:
There are no simple, unique word appearance inventory patterns for data blocks 23 through 27, 30 and 31. Therefore, if we use the above method, a more complex analysis would be required to establish block synchronization continuity of word pattern inventory through these data record blocks.
A more convenient yet reliable method of establishing record block number continuity for these last data record blocks can be established by using actual engineering values decoded by the NTSB from word 17, Fine Altitude. See NTSB Exhibit 8, (highlighted area).
Exhibit 8, a NTSB analog plot for the last portion of the flight, shows the altitude values incrementing smoothly and linearly at a rate near 20 to 30 feet per second. Had there been a disruption in the NTSB one-second data block sequence at this point in the FDR tape the slope of the analog plot would show this disruption by a step-change to the slope pattern. No such step-change is present and the contiguous sequence of NTSB data blocks is sufficiently proved without more laborious efforts. The NTSB reported two losses of synchronization of the playback FDR bit stream but both of these occurred several minutes earlier.
Accordingly, the NTSB Flight parameter word inventory record block patterns from Tabular Data No. 1 have been shown to faithfully "lock-step match" the word inventory patterns of the Superframe Block Nos. This perfect lock-step match of word patterns has been rigorously shown to extend over the last 19 contiguous data record blocks of FL 800.
Therefore, the last valid and decoded one-second data block appearing with time stamp 20:31:11 in NTSB Tabular Data No. 1 from FL 800 is the 31st sequential data block in Superframe 17!
The last word in data block 31 is always data word 6. Therefore, according to the NTSB Flight Parameter Tabular Data No. 1, Exhibit NTSB 7, the FL 800 data stream ended with data/documentation word 6 containing GMT hours (not printed on NTSB Tabular Data No. 1).
FL 800 FDR Magnetic Footprint Patterns Show Last Data Block as Block 35, Not 31
NTSB FDR Report critics refused to accept the "bit stream blending" explanation of FL 800 and FL 803 data at the end of the FL 800 FDR tape without more hard evidence. Knowledgeable and well researched critics requested the NTSB visually develop the magnetic footprints where the FL 800 FDR tape stopped operating when aircraft power was lost. The NTSB responded positively to this request. See NTSB Exhibit 9.
Exhibit 9 represented the first opportunity the NTSB critics had to inspect the actual bit stream waveform hard evidence at the end of the FL 800 FDR tape. All previous FDR data versions of the FDR data had been filtered, timed, edited and blended by the NTSB staff and their RAPS, Reproduce Analysis and Playback System.
Furthermore, the NTSB expanded the digital waveforms directly before the 3-inch erasure gap and actually identified the last several bits and words found on the FL 800 FDR tape. These expanded bit patterns were annotated with the NTSB announcement that the FDR tape ended with " bits 1 to 9 of word 4", GMT month, plus a block ending 8 bit postamble, 1000 0000.
But NTSB Exhibit 9 did not show a sufficient portion of the last FL 800 data record block to totally quiet the critics, who requested a FOIA tape copy of the last 30 data blocks before and the 30 data blocks after the FL 800 erasure gap.
When received, almost a year later, only a small and truncated 2 data record block set of waveforms immediately preceding the erasure gap was received. When asked why only 3.3 % of the requested FOIA data record blocks were supplied no explanation was received from the NTSB.
A strong complaint and threat of legal action against the NTSB quickly produced a full 60 plus data record block waveform set centered around the erasure gap, but copied from the FDR tape operated in the REVERSE play direction! Again, the NTSB FOIA submittal offered neither explanation nor even awareness that the waveform set was copied in a REVERSED from normal direction.
Nevertheless, despite significant bit stream waveform distortion from improper phase response equalization, sufficient evidence was gleaned from the FOIA waveforms to confirm the fact the last FL 800 data block before the erasure gap did in fact end at bit 9 of word 4 containing GMT month (not printed on NTSB Tabular Data No. 1).
This magnetic footprint hard evidence directly contradicted the previous evidence from Tabular Data No. 1, which had the last data block from FL 800 ending at word 6, GMT hour.
Superframe Data Block 35 always ends with word 4, GMT month. Data Block 31 always ends with word 6, GMT hour. See Exhibit GS -2. These events are always mutually inclusive.
NTSB Asked to Explain the Last Word 6 vs. Last Word 4 Contradiction
The NTSB was asked to explain why their Tabular Data No.1 word pattern groups from FL 800 ended with word 6 while their magnetic footprint patterns ended with word 4. In an unsatisfactorily response, the NTSB offered no understandable explanation, maintaining that their previous/erroneous published findings were now free of any error.
More FOIA requests were sent to the NTSB in an effort to specifically resolve the contradictions between the different ending-word patterns for the FL 800 FDR tape. These have yet to be received.
The initial FOIA 99-297 response from the NTSB arrived with an illicit "combination set" of waveforms and engineering values, which only furthered the interest in the word 6 vs. word 4 contradiction. This FOIA set of waveforms ended pictorially with word 4 and also ended with a set of decoded engineering values which exactly matched the values in Tabular Data No.1, i.e., a word pattern ending with word 6! This is a major mathematical contradiction to the 43 X 64 word Matrix used in FL 800 and cannot exist in this format.
The NTSB FOIA response thereby created even more and new word pattern contradictions. A data record block ending with word 4 must contain two word no. 27s (Pitch trim Stabilizer) and two word no. 28s (Aileron Position Inboard). But the last Tabular Data No. 1 and No. 2 show only 1 entry for each of these two parameters. See NTSB Exhibit 3B and NTSB Exhibit 10.
Additionally, certain characteristics of this FOIA set of waveforms did not identically match the waveforms from the magnetic footprint pictorials of NTSB Exhibit 9. Specifically, the amplitude modulation/erosion components present on the last 4 one-second data record blocks were vastly different. Also, the FOIA waveforms contained a new added waveform component, i.e., a large electronic transient spike 2/3rds of the way through the "blank tape" erase gap. The symmetry and shape of this spike is consistent with electronic editing. No such spike was present in NTSB Exhibit 9. See GS Exhibit -3 and -4.
These anomalies were responsible for more FOIA requests, which have not yet been honored by the NTSB.
9 , Fig. 3, Addendum 2, Sep.15, 1997
Data Blocks 32, 33, 34 and 35 exist but are withheld from the public by the FBI/NTSB.
There is clear and overwhelming hard waveform evidence that FL 800's FDR was properly functioning at least through the recording of Superframe 17, Data Block 35.
This fact was first revealed when the NTSB published Addendum 2 in Sep., 1998 in which they pictorially showed the last individual bits and word from the FL 800 FDR processed tape. In their zoomed and expanded view of the last portion of the FL 800 bit stream, in Fig. 3, they annotated the waveform ending with " Bits 1-9 of word 4", followed by the block-ending 8 bit postamble, 1000 0000. See Exhibit NTSB 9.
This flight-ending waveform bit and word pattern was again confirmed
when the NTSB responded to FOIA request 99-297 with a CD waveform copy
with the same bits 1-9 from word 4 preceding the last postamble from FL
800. The NTSB in their Feb. 15, 2000 FDR Final Report reconfirmed this
specific flight-ending word when their leading paragraph stated:
The ending of the FL 800 FDR tape at word 4 is tantamount to the tape ending at Superframe data block 35 as these two events are mutually inclusive. They cannot be separated. This point of irrefutable logic follows directly from the fact that 1) the FL 800 43 word flight parameter subframe is blocked into 64 word data record blocks on a first-come-first-served orderly basis and, 2) by definition Superframe 1 starts at Data Record Block 1 when subframe word 1 occupies word slot position 1 of the 64 data record block.
All versions of the NTSB Flight Parameter Tabular Data Charts No. 1 and No. 2 stop well short of Superframe 17, data block 35 -----they are completely blank after data block 31. These omissions leave 3072 FDR data bits unaccounted for from data blocks 32, 33, 34 and 35, which, if added to NTSB Tabular Data No. 1, would have been time stamped 20:31:12 through 20:31:15.
The proof that the NTSB tables are blank after data block 31 is a simple inventory or head counting of data blocks contained in the NTSB Tabular Charts. The 8 contiguous NTSB chart entries from CVR Ref. Times 20:30:53 to 20:31:00 can be clearly identified by unique word group appearance patterns as Superframe block nos. 13, 14, 15, 16, `17, 18, 19 and 20. There are only 11 more data block entries in the NTSB Charts, and 11 blocks added to block 20 is block 31. These facts are also irrefutable.
Therefore, the preceding analysis constitutes hard evidence consistent with the fact that the FBI/NTSB are knowingly withholding from the public over 3.000 flight parameter data bits from the end of FL 800. These 3,000 data bits from the last 4 seconds recorded on the FDR tape may well answer the question of what occurred during those last 4 seconds to cause the disintegration of TWA Flight 800.
NTSB Exhibit 1, Parameter List, p. 9, FDRFR Rev. 1, Feb. 15, 2000
NTSB Exhibit 2. MagnaSee Footprints, Fig. 2, FDR Add. 2, Feb. 15, 2000
NTSB Exhibit 5, p. 42, Tabular Data No. 1,Created Jan. 09, 1997; Report Feb. 28, 1997
NTSB Exhibit 6, p. 42, Tabular Data No. 1,Created Jan. 09, 1997; Add. 2, Feb.15, 2000
NTSB Exhibit 7, p. 42, Tabular Data No. 1, Rev Feb. 15, 2000; Rpt.Rev.1, Feb.15, 2000
NTSB Exhibit 8, Plot No.8, Report of Feb. 15, 2000
NTSB 9 Exhibit, Fig. 3, Addendum 2, Sep.15, 1997
NTSB 10 Exhibit,
p. 36, Tabular Data No. 2 Rev. Dec.22, 2000
GS Exhibit 1, TWA FL 800 Last Superframe Word Patterns, June 23, 2000
GS Exhibit 2, TWA Fl 800 Last Superframe Word Patterns-Extended, Jun. 23, 2000
GS Exhibit 3, AM Waveforms at Erase Gap, FOIA 99 - 297
GS Exhibit 4, Transient Spike in Erase Gap, FOIA 99 - 297
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