Fast rates of descent

[Mn1967]

There isn't a lot in the Internet about this question but hopefully someone will be able to on here. Flying from Detroit to Amsterdam in January 2015, we were straight and level at 40,000 feet. Somewhere over central Scotland we suddenly pointed downward at a relatively steep angle I've not experienced before. Checked out the flight on flight aware and found that we briefly descended at a maximum of 7135 fpm. I wonder how usual this is. Any ideas what might have precipitated it? I can't attach the photo but I've got a screen dump of the flight aware data.
Any ideas? Thanks in advance.

[Buster the Bear]

7,135ft per min, must have been an emergency or FR24 got it wrong again?

[Mn1967]

I cant verify the 7135 number but it felt like we went downhill very fast. I can however verify that the on board map showed us going from 40000 to 32000 in just a couple of minutes. Pilots made no announcements. The flight was DAL138 DTW AMS departed Detroit 31/12/14. I'm just curious - thought at the time perhaps there was some military activity which entailed us getting down fast. airspeed also went up very quickly and that does tally with flight radar track log.

It was an eventful trip - we started out of CUN the same day and had a 'no flaps' landing at DTW with full blue light services in attendance.

[BARKINGMAD]

Were you aboard?

If so, l would have thought that a real 7k+ downwards, even for a short time, would have been sensed proportionately in a pressurisation change, obvious to the ears of those aboard?

[DaveReidUK]

Depends how brief "briefly" was.

What was the net height loss?

[Mn1967]

We dropped from 40000 to 32000 in less than 2mns according to the map data on board the a/c. There was some ear popping but honestly not significant in my case. What was more noticeable for me was the pitch down which did feel significant. We then descended a bit more sedately through first layer of clouds to 28000. We also increased speed and what I was watching on board does tally with FR24 as we went from about 560/570mph to a max of 663mph. I attempted to work out where over Scotland and it looks as though it was over Cupar. Actual timing was 0902 local time on morning of 1/1/15 so I suspect the skies over Scotland were quite empty at that time.

[chevvron]

Sounds like a possible de-compression was detected by the crew; did the oxy. masks deploy?

[mathy]

Cupar?

Coo! Only 20 miles from Leuchars. Is that still occupied by the RAF? Were there any Bears about at Christmas?


Looks like the route included ERAKA where you would join airway UP58 to FINDO which is more less "Cupar". That ties in with onward routing via UM982 through lovely St Abbs beacon to ROKAN after which the muggers buddle for EHAM begins in earnest. So nothing stands out of the ordinary except activity near Leuchars perhaps


A "brisk" descent into Amsterdam with no delays would be 142 nautical miles from 41000 feet in 24 minutes in an A330-class aircraft.


Now only joking, my offsider who is a well-known wag says ATC asked "Why are you flying at 40000ft???". There then followed an expletive and normal service resumed at 39000ft. Only joking....


Hat, coat etc

[DaveReidUK]

FL400 to FL320 in around 2 minutes is approximately 4000 fpm, which is sporty but not particularly alarming, though in daylight 10° or so of nose-down pitch looks steeper than it actually is.

If it had been a decompression at that altitude, I'd have expected a rather more expeditious descent than that (it would have taken over 7 minutes to get down to FL100).

But it clearly wasn't a decompression, given that he levelled off at FL280 for a further 20 minutes.

[Hotel Tango]

We dropped from 40000 to 32000 in less than 2mns according to the map data on board the a/c. We then descended a bit more sedately through first layer of clouds to 28000.

Sounds like "DAL138 descend FL280 with best rate of descent until passing FL320".

[Nicolas7]

im pretty sure that he would mention if the oxygen masks had been deployed

[Mn1967]

Great posts, thanks all. I would have said 'no masks' but my post seems to have not made it through. You know, I wondered about Russian incursions Mathy...

ECAM surprise, are there any operational reasons that you could disclose that might fit the circumstances? In all other aspects it was a very normal flight. Not sure I could define sporty but other than the levelling out process that got a few people up from their beds, it wasn't jarring. Good a/c, good pilots and a somewhat different way to welcome in the new year over my homeland!

[Mr Mac]

I had a similar descent on Malaysian air lines from Borneo into KL in a 777 200 which had come down from Korea originally. We approached Malaysian Peninsula at 40k ft and did not start to lose height until over the coast, and it appeared as a passenger to be a very quick descent, although I could not post the figures as the original poster. I put it down to perhaps having ex military pilot, as we had blasted off from Kota K like a fighter, with sharp L/H turn at 5k ft approx. As this was in 2008 it must have been quite dramatic for it to stand out, as I have, and continue to do a lot of flying over the years.


Regards
Mr Mac

[Mn1967]

Thanks ECAM, good insights to a non pro... Non event always much more preferable than the alternative.