SQ321

 n 29/05/2024 15:26, Kelvin Davies wrote:
Hmm! Do I smell a rodent or a paint job (whitewashing). According to the news source which is always 101% accurate (smirk here) the BBC, Singapore Airlines has announced that the flight that went bump last week "dropped 178 feet over 4.6 seconds". Not a huge fall but I suppose significant enough to make your eyes water. It equates, in aeroplane terms to 2,321 ft/minute. Not actually that far out of the ordinary.

They then go on to quote the airline thus: "Their preliminary report said rapid changes in gravitational force (G) caused the altitude drop - which is just shy of the height of Italy's Leaning Tower of Pisa - and likely injured those who were not wearing seatbelts". Well, I never! Gravity was involved!

More from the airline: ""The rapid changes in G over the 4.6 seconds duration resulted in an altitude drop of 178ft (54m), from 37,362ft to 37,184ft," the report said. This is a rate of descent of -2321 ft/min.  Now we get into the whitewashing/fibbing bit. Data from ADSB shows the following time line:

At 08:06:42 it was flying at 37,000ft and the selected altitude on the Flight Management System was 36,992 ft, near enough to 37,000ft and there was 0 altitude change.

At 08:06:57 the altitude was 37,000ft but there was a change in the altitude selected on the FMS, when it was changed to 31,008ft. And therein lies the origins of the smell. Nobody is mentioning that. Someone changed the selected altitude on the FMS and the data was recorded before the plane had had to begin its descent to the newly selected altitude. The actual altitude was shown as 37,000ft with a rate of descent of 64ft/minute at this time but this is insignificant.

From 08:07:07 to 08:07:41 (34 seconds) the rate of descent starts changing rapidly through -512, 960, 1344, 1792, 2176, 2496 to 2,880ft/min

At 08:26:50, while still descending toward the selected altitude of 17,000ft, the FMS altitude was changed to 14,000ft.

Singapore Airlines's statement goes on to say "Approximately 17 minutes after the turbulence event, the pilots were able to make a "controlled descent from 37,000ft", the report said, adding the aircraft did not encounter any more severe turbulence during its diversion to Bangkok". I don't think even that is accurate. The plane reached the FMS altitude of 31,000ft after 3 minutes at 08:10:34. Next, the FMS altitude was changed to 17,000ft at 08:07:57 This was reached at 08:09:24. But at 08:26:50 while still descending at 20,800ft the next FMS altitude of 14,000ft was selected and this was reached at 08:31:47, 20 minutes after the intial upset. How approximate is "approximately"? Something else they don't mention is that the rate of descent reached -2496 ft/min. This is a bit faster than the rate reported by the airline of 2,321ft/min during the upset and this was while the pilots were in charge of the flight, not the weather, turbulence etc.

What do I think? I think it is entirely possible that the whole thing was kicked off when someone changed the FMS altitude to a level 6,000ft lower. But, that is only a possibility. Whatever the cause was, it seems to me we will never discover.

Finally, a piece about my experience with Singapore Airlines: In the late 1990s, I used to travel a lot to the Far East and I always used one of 3 airlines; Thai, Cathay Pacific and Singapore. They were the absolute dog's dangly bits. However, one night flying on a Singapore 747 from Singapore to Heathrow, we stopped at Bangkok. While on the ground, the driver announced we had burst a tyre on landing so there would be a small delay while they got the John Bull outfit out. Well, OK, they changed a wheel. We left in the dark with some fierce thunderstorms nearby. Shortly after take off, the seat belt and no smoking signs were switched off. About a minute later, the chief purser (a Sikh bloke) was called to the phone from the flight deck. His eyes went the size of dinner plates and he put down the phone, picked up the PA and announced in the most dramatic and obviously terrified manner that "We have a problem. Please return to your seats and observe the seat belt and no smoking signs" which had just come back on. The problem turned out to be the thunderstorm with some moderate turbulence which was no big deal. The memory of that purser's face still haunts me to this day and I vowed never to fly with Singapore again. And I never did!

So there!

 

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Time             Alt       Vert Rate   Wind Speed/   Squawk     FMS
                                (ft/minute)        Direction                 Alt Select
08:06:42     37000         0                 N/A               5213      36,992
08:06:57     37,000     -64            14/213               5213      31,008
08:07:07     36,925     -512          14/213               5213      31,008
08:07:11     36,875     -960          14/213               5213      31,008 282 miles to BKK
08:07:14     36,800    -1344         14/213               5213      31,008
08:07:16     36,750    -1792         15/216               5213      31,008
08:07:22     36,575    -2176         15/216               5213      31,008
08:07:32     36,175     2496         15/216               5213      31,008
08:07:41     35,775    -2880         15/216               5213      31,008 15 miles after incident
08:07:50     35,375    -2880         14/203               5213      31,008
08:07:55     35,175    -2432         14/203               5213      31,008
08:07:59     35,025    -1984         14/203               5213      31,008
08:08:10     34,650    -1984         14/203               5213      31,008
08:08:21     34,275    -1984         12/209               5213      31,008
08:08:32     33,900    -1984         12/209               5213      31,008
08:08:43     33,525    -1920         12/209               5213      31,008
08:08:55     33,175    -1920         12/209               5213      31,008
08:09:06     32,800    -1920         11/220               5213      31,008
08:09:17     32,400    -1920         11/220               5213      31,008
08:09:28     32,050    -1920         11/220               5213      31,008
08:09:40     31,675    -1920         11/220               5213      31,008
08:09:49     31,425    -1472         12/224               5213      31,008
08:10:03     31,125    -1152         12/224               5213      31,008
08:10:10     31,050    -704          12/224               5213      31,008
08:10:16     31,025    -256          12/224               5213      31,008
08:10:34     30,975    128          11/212                5213      31,008
08:17:49     31,000     0               5/240                5213      31,008
08:18:22     30,900    -896          5/240                5213      31,008
08:18:29     30,750    -1792         3/253               5213      16,992
08:18:32     30,650    -2240         3/253               5213      16,992
08:18:40     30,350    -2688         3/253               5213      16,992
08:23:57     23,425    -512           12/280             7700      16,992 Squawk 7700 1st time115 m to BKK
08:26:50     20,800    -1024         15/297              7700 14,297
08:29:24     17,250    -1728         8/306                7700     14,016
08:31:47     14,075    -2496         343/340        7700 11,008