AirAsia flight missing

[Peter Kesternich]

(...)However, there are other reports that the last radar contact (secondary only, primary had been already lost) had the plane at FL290 (lower than cleared, I'm guessing that in a descent some point after the photo described above).(...)

Hmmmmm... now I am wondering, how primary radar contact can be lost before secondary...

[Gabriel]

Hmmmmm... now I am wondering, how primary radar contact can be lost before secondary...

That's quite typical in fact.
Imagine the following.
Form all the power radiated by the radar, how much reaches the plane? (the farther the less, because the energy per sq ft is inversely proportional to the square of the distance) Of that, how much is actually reflected instead of absorbed? Of that, how much happens to be headed exactly back toward the radar? And how much actually reaches the radar? (again, inverse to the square of the distance).

With the secondary radar, however, no matter how much is reflected and how much reaches back the source. As long a the transponder detects the radar interrogation, no matter how fain was the signal, a fresh new, relatively powerful, radio signal (the response) is emitted from the plane.

There are whole airspaces that have only secondary radar coverage, because secondary radar is so much cheaper than primary. If you are only interested in airplanes with transponders, that's enough.

And with ADS-B, you don't even need a radar at all. Just send a generic omnidirectional interrogation signal and wait for the response. Or don't even send anything, just wait until the airplane's transponder is interrogated by a radar or another airplane's TCAS and "listen" to the response. That's how flight tracking sites work: A network of volunteers with a VERY inexpensive and small receiver connected to an even more inexpensive and small analog-digital converter connected to your PC where a free software decodes the data, and connected to the internet where you stream up the data to the site's server.

[AVION1]

Or had a massive airplane failure of some sort (due to weather, technical or human reasons).

It's hard to me to believe that weather alone can put the plane in an unrecoverable attitude (alone again).

The AF-type scenario, where a weather related "minor" incident is turned into a major disaster by the pilot's way of, hmmm..., "managing"... the situation is not crazy either.

Yes, sounds very similar to the AF accident. This is another Airbus, and here is my question. After the AF accident Airbus recalled all their airplanes so they would replace the old Pitot Tube assembly for a new style Pitot Tube, the old one was subject to icing. I wonder if Air Asia ever replaced their Pitot Tubes for the new ones after this Airworthiness Directive?

[orangehuggy]

speed 65 knots, descent rate 11.5k ft/min

[Gabriel]

Yes, sounds very similar to the AF accident. This is another Airbus, and here is my question. After the AF accident Airbus recalled all their airplanes so they would replace the old Pitot Tube assembly for a new style Pitot Tube, the old one was subject to icing. I wonder if Air Asia ever replaced their Pitot Tubes for the new ones after this Airworthiness Directive?

AF was an A330, AA was an A320. I don't know if these planes share the same pitot tubes or if the AD (airworthiness directive) included the A320.

The Thales pitot (that were fitted in AF) had a not-so-effective drainage that made it more prone to accumulate water that can then freeze. We don't know exactly how the AF pitots blocked, if it was due to liquid water freezing inside, supercooled water freezing on contact, or direct ice crystals blocking it. But while the Thales pitot was more prone to some forms of blocking, all pitots tubes are subject to the risk ob blocking in all forms if the conditions are severe enough. Pitots can be blocked, it happens relatively frequently (in aviation terms), this sometimes causes an unreliable airspeed situation (when 2 or more speed indications fiail) and pilots must be ready to fly without airspeed information, which is not difficult.

That said, I was intentionally ambiguous by saying "a weather related minor incident aggravated by the pilot's actions". It could be a pitot issue, an AoA frozen vane, an attitude upset, a windshear...

And still, I'm not even suggesting that it was weather related at all. Just saying that it would not be crazy finding.

[Gabriel]

speed 65 knots, descent rate 11.5k ft/min

Do you have the source?

[T.O.G.A.]

Or had a massive airplane failure of some sort (due to weather, technical or human reasons).

It's hard to me to believe that weather alone can put the plane in an unrecoverable attitude (alone again).

The AF-type scenario, where a weather related "minor" incident is turned into a major disaster by the pilot's way of, hmmm..., "managing"... the situation is not crazy either.

Or, simply engine flame outs plus, of course, weather.

[Evan]

Yes, sounds very similar to the AF accident. This is another Airbus, and here is my question. After the AF accident Airbus recalled all their airplanes so they would replace the old Pitot Tube assembly for a new style Pitot Tube, the old one was subject to icing. I wonder if Air Asia ever replaced their Pitot Tubes for the new ones after this Airworthiness Directive?

It's true that some of the AD's were specific to the A330/A340 and did not involve the A320. I remember how short-sighted this seemed to me at the time since they share common avionic architecture. However, the newer Thales AB pitots were found to also be unreliable in the presence of ice crystal ingestion and the phenomena has defeated Goodrich equipped Boeings as well. The only theoretical design solution is to provide a non-common backup sensor design such as the pitot plate sensors used on the B2 Spirit, but there was no industry discussion on this.

The issue was probably downplayed because these UAS incidents typically last about 30 seconds and pilots who do not upset the aircraft when taking manual control have been able to fly through these events and reestablish autopilot shortly thereafter.

The AF447 findings basically show that the UAS events are to be expected from time to time and the safety of the flight can be ensured by pilots well-trained in UAS procedure. So the solution lies in pilot skills, not probe design.

[Evan]

It's hard to me to believe that weather alone can put the plane in an unrecoverable attitude (alone again).

During the AF447 investigation, meteorological experts identified a 100mph updraft within the weather system they encountered. I think an A320 encountering that kind of shear, especially if initiating a rapid climb at the same moment, is going to experience sudden increase of AoA and g-loads perhaps well in excess of +3g and may even be elevated by the air mass above safe operational ceiling. I could see loss of control resulting from this or even structural failure. It also correlates to a rapid climb seen by ATC that appears to be beyond the aircraft's performance capability.

[Gabriel]

I'm going for a windshear of some kind putting them into an unrecoverable attitude.

It's hard to me to believe that weather alone can put the plane in an unrecoverable attitude (alone again).

... a 100mph updraft within the weather system they encountered. I think an A320 encountering that kind of shear, especially if initiating a rapid climb at the same moment, is going to experience sudden increase of AoA and g-loads perhaps well in excess of +3g and may even be elevated by the air mass above safe operational ceiling.

Maybe. But even then, I don't think it's an unrecoverable attitude (as long as the airframe holds in one piece of course).

[AVION1]

There is an AD for the A320 in regards to the pitot tubes:

Occurrences have been reported on A320 family aeroplanes of airspeed
indication discrepancies while flying at high altitudes in inclement weather
conditions. Investigation results indicated that A320 aeroplanes equipped with
Thales Avionics Part Number (P/N) 50620-10 or P/N C16195AA pitot probes
appear to have a greater susceptibility to adverse environmental conditions
than aeroplanes equipped with certain other pitot probes.
Prompted by earlier occurrences, DGAC France issued AD 2001-362 to
require replacement of Thales (formerly known as Sextant) P/N 50620-10 pitot
probes with Thales P/N C16195AA probes.
Since that AD was issued, Thales pitot probe P/N C16195BA was designed,
which improved airspeed indication behaviour in heavy rain conditions, but did
not demonstrate the same level of robustness to withstand high-altitude ice
crystals. Based on these findings, EASA have decided to implement
replacement of the affected Thales probes as a precautionary measure to
improve the safety level of the affected aeroplanes.
Consequently, EASA issued AD 2014-0237, retaining the requirements of
DGAC France AD 2001-362, which was superseded, to require replacement
of Thales Avionics pitot probes P/N C16195AA and P/N C16195BA.

Here is the link:
http://ad.easa.europa.eu/ad/2014-0237R1

.........................................................................................................................

AD No.: 2014-0237R1
Date: 05 December 2014
Note: This Airworthiness Directive (AD) is issued by EASA, acting in accordance with
Regulation (EC) No 216/2008 on behalf of the European Community, its Member States and of
the European third countries that participate in the activities of EASA under Article 66 of that
Regulation.
This AD is issued in accordance with EU 748/2012, Part 21.A.3B. In accordance with EC 2042/2003 Annex I, Part M.A.301, the
continuing airworthiness of an aircraft shall be ensured by accomplishing any applicable ADs. Consequently, no person may operate
an aircraft to which an AD applies, except in accordance with the requirements of that AD, unless otherwise specified by the Agency
[EC 2042/2003 Annex I, Part M.A.303] or agreed with the Authority of the State of Registry [EC 216/2008, Article 14(4) exemption].

[Gabriel]

Good finding!

That said... December 2014? If this plane had been fitted with one of the rogue Thales probes, chances are that this AD had not been implemented yet:

From your link:

Revision 1: 12 December 2014
Original issue: 12 November 2014

Within 48 months after 12 November 2014 [the effective date of the
original issue of this AD], replace each Thales pitot probe P/N C16195AA
and P/N C16195BA in accordance with the instructions of Airbus SB
A320-34-1170.

[Peter Kesternich]

Or, simply engine flame outs plus, of course, weather.

A situation like that would normally still allow the pilots to make radio contact and communicate the emergency. What happened to QZ8501 must have been a) sudden and b) so severe that the pilot's couldn't report it.

[ultraflight]

Gabriel:
"Form all the power radiated by the radar, how much reaches the plane? (the farther the less, because the energy per sq ft is inversely proportional to the square of the distance)"

I think a radar antenna usually is a parabolic one, sending out a much more concentrated beam that an omnidirectional transmitter.
The inverse-square law generally applies when some force or energy is evenly radiated outward from a point source in three-dimensional space.

[brianw999]

Maybe. But even then, I don't think it's an unrecoverable attitude (as long as the airframe holds in one piece of course).

I've been thinking that I should have quantified that statement by adding the words "unrecoverable attitude by the Crew of the subject aircraft. in other words, unrecoverable by this particular crew.
Whatever actually happened I don't like to even think about what the passengers experienced as they fell vertically at almost 130mph. Somewhere around three minutes worth of sheer terror.