We have analysed the raw data from the transponder of #4U9525 and found some more data apart from the regular position/altitude data.
These are the decoded ModeS (Downlink Format 20) frames which contain replies to interrogating radar requests (Upling Format 20).
09:30:48Z.651 MCP/FMC ALT: 38000 ft QNH: 1006.0 hPa
09:30:48Z.936 T,3c6618,43.115341,5.671181,38000,GWI18G
09:30:49Z.496 T,3c6618,43.116028,5.671692,38000,GWI18G
09:30:50Z.076 T,3c6618,43.117381,5.673065,38000,GWI18G
09:30:50Z.111 MCP/FMC ALT: 38000 ft QNH: 1006.0 hPa
09:30:50Z.553 MCP/FMC ALT: 38000 ft QNH: 1006.0 hPa
09:30:50Z.619 MCP/FMC ALT: 38000 ft QNH: 1006.0 hPa
09:30:50Z.626 T,3c6618,43.118408,5.673736,38000,GWI18G
09:30:51Z.127 T,3c6618,43.119095,5.674247,38000,GWI18G
09:30:51Z.636 T,3c6618,43.120453,5.675092,38000,GWI18G
09:30:52Z.386
MCP/FMC ALT: 38000 ft QNH: 1006.0 hPa
09:30:52Z.567 T,3c6618,43.122208,5.676482,38000,GWI18G
09:30:53Z.036 T,3c6618,43.122894,5.676993,38000,GWI18G
09:30:53Z.546 T,3c6618,43.124271,5.678166,38000,GWI18G
09:30:54Z.083
MCP/FMC ALT: 13008 ft QNH: 1006.0 hPa
09:30:54Z.096 T,3c6618,43.125295,5.678689,38000,GWI18G
09:30:54Z.676 T,3c6618,43.125961,5.679421,38000,GWI18G
09:30:55Z.156 T,3c6618,43.127157,5.680259,38000,GWI18G
09:30:55Z.397
MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:30:55Z.453 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:30:55Z.636 T,3c6618,43.128367,5.681109,38025,GWI18G
09:30:56Z.186 T,3c6618,43.129211,5.681656,38025,GWI18G
09:30:56Z.707 T,3c6618,43.129898,5.682167,38000,GWI18G
09:30:57Z.267 T,3c6618,43.131626,5.683201,38000,GWI18G
09:30:57Z.312
MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:30:57Z.836 T,3c6618,43.132507,5.684020,38000,GWI18G
09:30:58Z.050 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:30:58Z.296 T,3c6618,43.133011,5.684403,38000,GWI18G
09:30:58Z.767 T,3c6618,43.134559,5.685425,38000,GWI18G
09:30:59Z.216 T,3c6618,43.135397,5.685948,38000,GWI18G
09:30:59Z.746 T,3c6618,43.136261,5.686575,38000,GWI18G
09:30:59Z.988 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:00Z.146 T,3c6618,43.137451,5.687149,38000,GWI18G
09:31:00Z.165 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:00Z.676 T,3c6618,43.137817,5.687660,38000,GWI18G
09:31:01Z.676 T,3c6618,43.139866,5.689022,38000,GWI18G
09:31:02Z.027 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:02Z.238 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:02Z.496 T,3c6618,43.141402,5.690199,38000,GWI18G
09:31:03Z.030 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:03Z.456 T,3c6618,43.143494,5.691429,38000,GWI18G
09:31:04Z.376 T,3c6618,43.145731,5.692945,37975,GWI18G
09:31:04Z.943 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:05Z.346 T,3c6618,43.147430,5.693984,37975,GWI18G
09:31:05Z.558 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:05Z.993 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:06Z.466 T,3c6618,43.149828,5.695365,37975,GWI18G
09:31:07Z.164 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:07Z.346 T,3c6618,43.151367,5.696539,37950,GWI18G
09:31:08Z.256 T,3c6618,43.153427,5.697752,37950,GWI18G
09:31:08Z.776 T,3c6618,43.154111,5.698308,37925,GWI18G
09:31:09Z.276 T,3c6618,43.154995,5.698962,37925,GWI18G
09:31:09Z.712 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:09Z.960 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:10Z.326 T,3c6618,43.157364,5.700307,37925,GWI18G
09:31:11Z.312 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:11Z.467 T,3c6618,43.159607,5.701713,37900,GWI18G
09:31:11Z.876 T,3c6618,43.160660,5.702415,37900,GWI18G
09:31:12Z.102 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:12Z.386 T,3c6618,43.161512,5.702885,37875,GWI18G
09:31:12Z.846 T,3c6618,43.162211,5.703408,37875,GWI18G
09:31:13Z.316 T,3c6618,43.163049,5.704128,37875,GWI18G
09:31:13Z.896 T,3c6618,43.164597,5.704970,37875,GWI18G
09:31:14Z.401 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:14Z.493 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:15Z.536 T,3c6618,43.168030,5.707201,37825,GWI18G
09:31:16Z.416 T,3c6618,43.169380,5.707921,37825,GWI18G
09:31:17Z.028 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:17Z.266 T,3c6618,43.171288,5.709294,37800,GWI18G
09:31:18Z.196 T,3c6618,43.173019,5.710144,37775,GWI18G
09:31:19Z.166 T,3c6618,43.175385,5.711648,37750,GWI18G
09:31:19Z.262 MCP/FMC ALT: 96 ft QNH: 1006.0 hPa
09:31:20Z.176 T,3c6618,43.177277,5.712891,37725,GWI18G
09:31:21Z.216 T,3c6618,43.179202,5.714068,37700,GWI18G
Between 09:30:52 and 09:30:55 we can see that the autopilot was manually changed from 38,000 feet to 100 feet and 9 seconds later the aircraft started to descend, probably with the "open descent" autopilot setting.
The reason why the selected altitude is 96ft is that least significant bit for altitude setting equals 16 ft, and we suspect that you can’t set autopilot to 0000 altitude, so the minimum would be 100ft down rounded to 96ft in binary representation in BDS40h register.
Any comments or thoughts about this?
Playback:
http://www.flightradar24.com/data/fl...u9525/#5d42675
This data has also been handled over to BEA 2 days ago.