PPRuNe Forums - View Single Post - BREAKING NEWS: airliner missing within Egyptian FIR
Old 4th Nov 2015, 10:13
  #805 (permalink)  
Join Date: Jul 2002
Location: Confusio Helvetica
Posts: 299
reading tea leaves

Folks, here's the rules:
1. At the moment, there's a lot of pressure on the press to report _anything_ that can conceivably be associated with this accident. As a result individual "unconfirmed sources", especially from the Tabloids, cannot be used for anything.

2. The FR24 data: They've now come out and given all the information you need: after the first moment, their data is unreliable. Altitude is given by GPS. GPS is not designed to give altitude; if you doubt me, download an app that spits out the raw data from your phone's GPS unit. Lat and Longitude will be precise, but altitude will be all over the place. To get precise information, most terrestrial navigation systems use something else, like looking up Lat. and Longitude on a Digital Elevation Module database.
Certainly, with enough time and controlling for enough factors, you *might* be able to fit that GPS data into a model of the aircraft's altitude. But spikes and other garbage are just not going to work. So, at the moment, the FR24 data are useless.

3. Rear Pressure Bulkhead. Yes, this was is what failed in JAL 123, and in whatever that Viscount crash in Belgium was. I haven't seen it credited with China Airlines 611, however. That was simply structural failure from an improper tailstrike repair. There seems to be a mindset: "Tailstrike = RPB failure", and that's dangerous.

4. A321 and tailstrikes. A321s have the longest bodies of the A320 family, and tailstrike with some frequency. When they do, they don't strike back at the RPB, but further forward. For example, someone scraped this a321 pretty bad, with the center of damage just below the Bulk Cargo Door. This means that, even if the 2001 repair were done perfectly, some other tailstrike might have doomed this aircraft. We've seen here the reports of pilots "not hearing" a tailstrike.

Now, to the tea leaves:

What we do have from the FR24 and the debris field is an aircraft that broke apart while climbing through 30,000 feet. From the photographs, the tail section separated from the rest of the aircraft, and the tail section itself seems to have broken into two parts: one part with the APU and tail cone neatly sheared, the other with half the VS, neatly sheared from the windows to the top along FR65, and, on the bottom, tearing down and forward of FR65 through the rearmost two windows and down to the Bulk Cargo Door (which isn't attached). This tail section is laterally symmetrical: left and right show more or less the same tearing. The horizontal stabilizers have been sheared clean, suggesting that they suffered excessive aerodynamic pressure.

Accidents on initial climb favors pressurization-related events: Fuselage cracks from metal fatigue, improper tailstrike repairs, door failure, and, sure, bombs rigged to cabin altitude. They all occur in this zone.
While any of these are possible, only one is favored by the information we have available.
DingerX is offline