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!
Sheet1
Page 1
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