S7 A321 Unreliable airspeed event, Magadan, 02 Dec 2021

[FullMetalJackass]

Not seen this one announced here but the plane, an S7 A321, took off from Magadan and got into issues.... apparently the autopilot system disconnected, there was an onboard electronics failure and the fuselage was covered in ice - five minutes after taking off from Magdan airport in eastern Russia.

The captain declared a Mayday but pilots were unable to dump fuel and land in the departure airport, despite circling overhead several times. Instead, they were forced to fly on over mountain ranges, towards the next nearest airport Yakutsk before finally landing in Irkutsk five and half hours later as the temperatures in Yakutsk were -30, but only -1 at Irkutsk

Anyone got any more info?

[DaveReidUK]

The pilots' reported inability to dump fuel might have something to do with the fact that they were flying an A321.

[FullMetalJackass]

You learn each day. But coming back to the incident, they first circled over the airport a number of times, then elected to go to another nearby airport where they saw it was even colder and risk of ice was more severe so they flew further where It took them - apparently - 3 hours to reach their cruising altitude at which time they'd burnt off so much fuel that they couldn't reach their destination of Novosibirsk.

[FlightDetent]

Ice builds from liquid water. If your choice is only sub-zero temperatures, broadly speaking , colder is better.

[Bandures]

Could you change the topic name? It's misleading. If you don't have any information apart from what you've posted, how can you say "incorrect / counterfeit de-icing fluid"?

[Cough]

Incident on AvHerald (https://avherald.com/h?article=4f10cac3&opt=0)

Guessing the deicing fluid used doesn't has much to do with this... It will never protect the aircraft after the takeoff roll is started.

[B2N2]

This sounds like deicing fluid may have been applied around pitot and static ports.

[Clandestino]

The idea that ground de-/anti-icing had something to do with the incident can be safely disregarded. If one has really bad case of iced wing one either: 1) fails to get airborne 2) gets airborne but then mush in ground effect until hitting the obstacle 3) stalls after leaving ground effect 4) gets wing ice ingested by tail mounted engines with consequential trust loss. Since this birdie has flown for hours, obviously it left ground effect at the good side of the trust curve. Even if the aeroplane was not de-iced properly, the aerodynamic effect of contamination was not enough to induce the upset.

Now, there is a picture making circles and it's been claimed it represents the QAR readout of the incident flight. Provided it's real, the triggering event was control law degradation to ALT1. I cannot figure out what caused it; G trace doesn't show any significant turbulence while left and right IAS and baro alt are consistent all throughout the upset. There are intermittent faults of both yaw dampers, but they got recorded later, before and after the wildest of gyrations. It looks like F/O was PF but the captain took over the controls and pushed the nose down, reaching minimum of -8.2°, before pulling up to about 30. Some interesting pitch, roll and speed excursion followed, probably helped by large and alternating stick displacement. Picture resolution is too low to figure out whether occasional dual input exacerbated or damped the ride. Control law degraded to direct but restored to ALT1 after about five minutes. There were some stall, some overspeed and some unspecified red warnings. Eventually everything settled down.

[FullMetalJackass]

Bandures

Because the report I read said the authorities were investigating the fact that it was something to do with the deicing fluid used.....

[Less Hair]

How long did they fly in direct law?

[Clandestino]

About five and half minutes.

[MissChief]

Direct Law....so what?

I've landed a 321 in Direct Law, after a longish straight-in approach. No biggie. (Caused by port icing initially, hours before)

[pattern_is_full]

Rosaviatsia updates Dec. 9 -

- aircraft suffered ADR #1, #2, #3 faults after takeoff, resulting in large excursions in roll and pitch
- aircraft was deiced in two stages. Type I fluid, then type IV. Fuselage was NOT deiced, only airfoils.
- Suggestion that snow on fuselage, in particular cockpit windows, melted once window heat was turned on. This continued during taxiing.
The runoff then froze again lower on the nose, disrupting airflow to the pitot tubes.

Incident: S7 A21N at Magadan on Dec 2nd 2021, unreliable airspeed (http://avherald.com/h?article=4f10cac3&opt=0)

[Magplug]

I have personally experienced airspeed fluctuations due to heavy icing whilst going round in the hold in UK at around FL100. The aircraft was in a steady state with a known power set. My (LHS) airspeed fluctuated 50kts or more over a period of 30 seconds whilst IAS 2+3 remained reading the same steady state. I considered executing the UAS abnormal procedure but with traffic in the hold both above & below us I considered doing nothing was the safest option. My only action was to retard the thrust levers to current power & disengage the ATHR to make sure there was no ATHR misbehaviour. After 60-90 seconds we made VMC and all indications went back to normal. The aircraft remained in normal law throughout. During the encounter we picked up serious amounts of icing around the windscreen.

[Less Hair]

Imagine this with a single pilot cockpit or even unmanned aircraft.

[FlightDetent]

Imagine this with a single pilot cockpit or even unmanned aircraft.The initial actions are not exactly Mars orbiter logic. Without coherent speed data:
= wings level + N1 60% + N.U. 6°

Whereas the report will have 4 pages on why the crew couldn't do exactly that.

​​​​​​​

[vilas]

Imagine this with a single pilot cockpit or even unmanned aircraft.
The single pilot in cockpit, let's say in A350 will just watch the aircraft inform him that it has automatically changed to backup speed which is mathematically derived synthetic speed not requiring any pitot static data. So what's the problem? Also even with triple ADR problem control laws stay in alternate law but without any protection. Only with gear down will go to direct law.

[Less Hair]

90 degrees of bank are the problem. No reliable data to feed the systems or displays and an airframe moving to raw physical flight with maybe one stalled wing or similar.

[arf23]

Given all the problems caused by pitot tubes over the years (AF447,2xMAX) and more, surely there must be better technology that perhaps an air-computer could compare pitot readings to, see if it's likely the aircraft is in icing conditions or the pitots are just plain likely to be giving duff info, then suggest to the pilots to switch to an alternate system until the disagree is resolved?

[Nightstop]

Brilliant suggestion arf23, I wonder why Airbus never thought of that..

[tdracer]

Given all the problems caused by pitot tubes over the years (AF447,2xMAX) and more, surely there must be better technology that perhaps an air-computer could compare pitot readings to, see if it's likely the aircraft is in icing conditions or the pitots are just plain likely to be giving duff info, then suggest to the pilots to switch to an alternate system until the disagree is resolved?

The MAX issues had nothing to do with pitot probes.
Keeping pitot probes clear of ice isn't rocket science - but it takes lots of electrical power (engine inlet probes are around 500 watts, the aircraft probes are even more). Problem starts when designers try and reduce that electrical load to better optimize the aircraft as a whole.

[CaptainMongo]

Here is a Safety First unreliable speed article:


https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/unreliable-speed.pdf

[giggitygiggity]

Given all the problems caused by pitot tubes over the years (AF447,2xMAX) and more, surely there must be better technology that perhaps an air-computer could compare pitot readings to, see if it's likely the aircraft is in icing conditions or the pitots are just plain likely to be giving duff info, then suggest to the pilots to switch to an alternate system until the disagree is resolved?
They've done that already. NAV ADR Disagree and the Reversible BUSS (Back up Speed Scale).


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1573x1125/buss_c151281c9a61f1539613f61d63ab1bc7c3b7c455.jpg


https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/668x404/buss2_b00a27cc84a79172285bc28ee11fd4736af865d3.jpg

[punkalouver]

The aircraft had been parked in conditions of heavy downpour and temperatures between -9 and -12 degrees Centigrade. The flight crew initiated de-icing of wing and stabilizer upper surfaces, but did not request the fuselage to be de-iced. Type I fluid was first applied followed by type IV fluid. The aircraft departed at a takeoff weight of 89315kg (MTOW 93500 kg) and a CG at 25.3% MAC well within all limits. In the initial climb as result of disagreeing airspeeds the aircraft control systems switched from normal mode to direct mode for the roll channel and alternate mode for the pitch channel, the autopilot disengaged. A second after the autopilot's disengagment the stall warning sounded. The crew took manual control of the aircraft. The differences in the speed readings increased further. 5 minutes after takeoff the crew declared Mayday reporting unreliable airspeed, decided to return to Magadan and stopped the climb at 8900 feet MSL. Descending through 4800 feet MSL on approach to Magadan the indicated airspeed increased to 370 KIAS causing an overspeed warning prompting the pilot flying to pull back on the side stick resulting in a climb at a rate of 17300 feet/minuate. The aircraft reached 13800 feet MSL and stalled. After regaining control the crew attempted an approach to Magadan but reported they were not in a position to land and went around. The crew subsequently decided to divert to Yakutsk. While enroute to Yakutsk S7's control center sent a message recommending to divert to Irkutsk where the aircraft ultimately landed.

Rosaviatsia analysed that the snow condition was "fluffy", not wet. The crew, not contradicted by ground crews, thus considered the snow on top of the fuselage would be just blown off during takeoff. Magadan Airport has no possibility to blow snow off with compressed air. The crews did not consider that the snow on the windshield would melt and run down as water the sides of the fuselage where the water would freeze again and form a "barrier" in front of the pitot tubes. The remains of barrier ice however were discovered after landing in Irkutsk. The FCOM warns of snow melting on the windscreen when the window heating if forced on rather than set to automatic - the window heat switch was on throughout the flight, it could not be established, when it was moved into the on position.

Rosaviatsia analysed that after descending to about 5300 feet (standby altimeter showed 4090 feet MSL) while attempting to return to Magadan the aircraft's pitch stabilized at +10 degrees, the aircraft experienced a vertical acceleration of +2G and the aircraft began to climb again. Thrust was set to 90%. Subsequently there were synchronous control inputs by both pilots deflecting their side sticks to the maximum left/right positions attempting to limit the roll of the aircraft between +/- 42 degrees of bank angle. There were no rudder movements, this however may indication disconnection of the yaw control channel. In the 42 seconds following the thrust being set to 90% the aircraft climbed rapidly and encountered roll oscillations between -90 degrees and +47 degrees with vertical accelerations between -0.5 and +1.9G. The angle of attack remained fairly stable throughout that time at 10 degrees +/- 5 degrees nose up.

After the first officer stopped providing control inputs the captain was able to stop the roll oscillations and stabilized the heading about a minute later, pitch oscillations remained however. 4 minutes after the onset of the upset the crew finally moves the stabilizer, which had remained at 9.3 degrees at that time, to 7.5 degrees, the pitch angle begins to decrease and the stall warning ceases. About 12 minutes after the onset of the upset the flight crew regains full control of the aircraft and begins to control the aircraft with the assistance of the FMGS again.

The report concludes the probable causes of the serious incident were:

a combination of following factors:

- non compliance with the clean aircraft concept by the aircraft crew and ground personnel in organizing and performing de-icing; as result snow was not removed from the forward fuselage (on and under the cockpit glazing) the melting during taxi and takeoff of which caused "barrier ice" in front of the pitot tubes, distortion of air flow and switching the control system's roll channel to DIRECT and the pitch channel to "ALTERNATE" mode.

- while flying the aircraft in degradated control mode the pilot made disporportionate control inputs which caused the aircraft to stall. When the aircraft stalled and got into a difficult spatial position, both captain and first officer made control inputs (dual control) which are prohibited by the FCOM and made it difficult to return the aircraft into operational flight modes and thus increased risk to safety.

- the decision to initiate de-icing by flight crew and ground personnel were done in heavy snowfall conditions which leave no time for protective action by the de-icer

- only 99 liters of type IV deicing fluid were used despite the recommended 230 liters for the A321 Neo

- the dynamic viscosity of the type IV de-icing fluid deviated at 20 degrees C (1860 mPas instead of 2000 mPas). Reduced dynamic viscosity results in lesser retention on the aerodynamic surfaces of the aircraft and may increase the risk of ice on critical surfaces.

[inducedrag]

Does A321 do have option for fuel dumping?

[oceancrosser]

Does A321 do have option for fuel dumping?

Would it offend you if it was suggested reading through this short thread before posting? The answer might already be there…and you don’t have to read far.

[ManaAdaSystem]

If you have snow and ice on the windshields and switch on the probe/window heat (that is the procedure in cold weather), it will take just a few minutes for this to melt and run down the sides of the aircraft and then refreeze. As in you switch it on and walk out for the external inspection and see a nice layer of rippled clear ice that will make your day really bad if you don*t remove it. The system will come on automatically after the first engine start. If the crew fails to switch on the window heat and just use the wipers to clear the snow, the melt and refreeze will take place after first engine start and with both pilots inside the aircraft.
And the fun starts at lift off if you don*t catch any airspeed issues during takeoff.

[Sailvi767]

What happened to pitch plus power equals performance?