FMS failure leads to Citation crash?

JimNtexas

JimNtexas

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Jim - In Texas!
I noticed this NTSB preliminary of a Citation Cj1 fatal on Kathryn's Report:

Initial air traffic control data indicated that shortly after takeoff and while proceeding southbound, the pilot reported that he had experienced a Flight Management System (FMS) failure, and that he needed to fly straight and climb while he tried to program the backup FMS.

The controller then instructed the pilot to climb to flight level 310, or 31,000 feet mean sea level, as well as provided the pilot with vectors around light precipitation. Shortly thereafter, the pilot declared a MAYDAY, stated that he was having difficulty with the backup FMS, and that he was hand-flying the airplane.

At this time the controller issued the pilot a no-gyro turn to the left to avoid precipitation, after which the airplane's airspeed was observed to fluctuate significantly. The airplane was then observed turning to the right before the radar target was lost. There were no further transmissions from the accident airplane.
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I know we have some Citation pilots here. Could an FMS failure cause the primary attitude display to fail? Would an FMS failure disconnect the autopilot?

Is there a failure mode of the FMS that could result in loss of aircraft control?

I don't want to pile on a pilot who isn't here to tell his side of the story, I'm just trying to figure out what might have caused this possible loss of control accident.
 
It looked to me like in this serial # airplane that most if the radio and instruments are powered by an AC inverter. There are two, one standby and the other in use and required crew intervention to switch to the standby. Wether or not this system was a factor is unknown
 
From reading the prelim report, it sounded to me more like he had some extensive avionics problems, and hand-flew the airplane into a thunderstorm while preoccupied with the FMS.
 
airguy said:
From reading the prelim report, it sounded to me more like he had some extensive avionics problems, and hand-flew the airplane into a thunderstorm while preoccupied with the FMS.
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It will never be known what instruments (if any) actually failed, what instruments the pilot wrongly believed to be malfunctioning, and what instruments were actually working properly.

Some combination of the above likely occurred. He wouldn't have broken up the aircraft otherwise.
 
Hand-flying a CJ on a vector while staring at the backup AI and DG should be a no-op for an experienced pilot. I wonder how much the FMS pre-occupation distracted him from the hand-flying task.
Golden rule of piloting: aviate-navigate-communicate.
 
Could an FMS failure cause the primary attitude display to fail?
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No. I have turned ours off in flight and the eadi continues to provide attitude information.

Would an FMS failure disconnect the autopilot?
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I don't think so but will have to try it again to be sure. However, even if the A/P kicks off, the airplane doesn't do anything wild.

Is there a failure mode of the FMS that could result in loss of aircraft control.
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Not that I have been taught, experienced, or heard of. You can turn the FMS off in flight and nothing untoward is going to happen.


Jim, these answers are from my experience with a Ce-525 which is ~70 serial numbers away from the accident aircraft, with the Honeywell SPZ5000 autopilot and the GNS-XLS FMS installed; other configurations are possible.
 
BigBadLou said:
Hand-flying a CJ on a vector while staring at the backup AI and DG should be a no-op for an experienced pilot. I wonder how much the FMS pre-occupation distracted him from the hand-flying task.
Golden rule of piloting: aviate-navigate-communicate.
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:yes:....
 
airguy said:
From reading the prelim report, it sounded to me more like he had some extensive avionics problems, and hand-flew the airplane into a thunderstorm while preoccupied with the FMS.
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What thunderstorm??:confused::confused:
 
While the LiveATC feed didn't capture every communication between the accident pilot and ATC, what it did record seems different than what is presented in the Prelim. Shortly after the accident, I transcribed what was available on the feed.

21:37 [RECORDING TIME] - N711BX: Departure, Citation 7-1-1-bravo-x-ray passing 7,500 for 10,000 with you.

21:45 - ATC: Citation 7-1-1-bravo-x-ray, Salt Lake departure. Radar contact, climb and maintain flight level 2-3-0, delete speed restriction.

21:49 - N711BX: Climbing to 2-3-0, ah, 7-1-1-bravo-x-ray, I am in a straight CJ, limited to, ah, certain amount of speed.

22:00 - ATC: Citation 1-bravo x-ray, tell you what, just maintain 1-4-thousand for now, 14,000 and delete all speed restrictions. What are you going to climb out at?

22:08 - N711BX: Climbing right now at 200 knots, 7-1-1-bravo-x-ray, climbing to 1-4 thousand.

22:12 - ATC: 1-bravo x-ray, thanks.

...

23:27 - ATC: Citation 1-bravo-x-ray, I'll have higher for you in 20 miles.

23:31 - N711BX: 7-1-1-bravo-x-ray, I appreciate that.

...

25:00 - ATC: ---You need any assistance?

25:05 - N711BX: Autopilot failure, would like to climb out of, uh, the weather right now but I am descending to 14,000 feet but I would request a climb to whatever altitude straight ahead.

...

25:55 - N711BX: ---[unintelligible, possibly "horizon"] climbing 1-8-thousand, ah, my number 2 is working, and, um, just my altitude, ah, failed. So, uh, but number 2 is working, climbing to 1-8-thousand.

26:10 - ATC: Okay, 1-bravo-x-ray, there's going to be traffic that's gonna cross above you at flight level one-niner-zero, so it's very important that you stop at flight level 1-8-0, 1-8-0 on the altitude.

26:10 - N711BX: We'll be watching, 711BX.

26:22 - ATC: 1-bravo x-ray, there's, um, I'm showing you splitting two cells of light precipitation on your present heading, and now I'm showing light precipitation at your 12 o'clock at 1-5 miles, it's about six miles along your route of flight. Do you need vectors to, uh, clear weather?

26:38 - N711BX: I would appreciate any vectors possible. [Stuck mic captures sound of deep breaths]

26:42 - ATC: Okay, November 1-bravo-x-ray, I need you to paint a picture for me, where do think the clearest skies would be? I can vector you wherever you need to go.

26:50 - N711BX: I'm heading to Tucson, my altitude will not hold right now, um, so I am hand fly--- [Cuts off]

...

27:12 - ATC: November 1-bravo-x-ray, I had you on a stuck mic there for a second. I'm showing you at 1-7-thousand, five hundred. Just fly your present heading, just fly straight ahead, and there should be, um, no precipitation in about four miles. There's an RJ five miles southeast of you, he's at flight level 1-9-0, and he is IMC.

27:29 - N711BX: Okay, MAYDAY, I do need to get up higher, 7-1-1-bravo-x-ray. Um, I am losing, ah, different instruments. I'd really like to get into clear weather.

27:39 - ATC: 1-bravo-x-ray, climb now maintain flight level 2-3-0, flight level 2-3-0 on the altitude.

27:45 - N711BX: Climbing to 2-3-0, 7-1-1-bravo-x-ray.

...

28:22 - N711BX: ---Operating correctly.

28:23 - ATC: November 1-bravo-x-ray, 'kay, I show you through 20.2 now, and, uh, do you want to continue on to Tucson?

28:28 - N711BX: That is affirmative.

28:30 - ATC: November 1-bravo-x-ray, turn left, it's a no-gyro vector to the south-southeast.

[No further response from N711BX recorded on frequency]

29:43: ATC: November 7-1-1-bravo-x-ray, Salt Lake approach. Ident if you hear this transmission.

****

It will be interesting to see what comes out from the investigation.
 
To answer your question, I tried this yesterday: turning off the FMS does not disable the autopilot...it still maintains altitude commands. However if you are in FMS (vs VOR) and nav mode (vs heading) it will lose all lnav info. It 'coasts' on the last heading provided by the FMS, indefinitely.
 
Let'sgoflying! said:
No. I have turned ours off in flight and the eadi continues to provide attitude information.


I don't think so but will have to try it again to be sure. However, even if the A/P kicks off, the airplane doesn't do anything wild.


Not that I have been taught, experienced, or heard of. You can turn the FMS off in flight and nothing untoward is going to happen.


Jim, these answers are from my experience with a Ce-525 which is ~70 serial numbers away from the accident aircraft, with the Honeywell SPZ5000 autopilot and the GNS-XLS FMS installed; other configurations are possible.
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Hi! I'm just a GA pilot with Commercial/Instrument Airplane and CFI certificates and only 380 hours total flight time, but this accident has piqued my curiosity. Could you tell me, in a general sort of way, what the cold-weather/icing conditions operations would be for the accident aircraft in this flight? I think I can safely assume that such a plane has pitot/static port heat and all sorts of fancy anti-icing equipment for wings, engines, other critical components &c. Are these systems automated in a plane like this, or would they have been pre-takeoff checklist items that had to be manually engaged? Could these have been overlooked, as crazy as it sounds? It is apparently known from the accident report that this plane very likely flew through an icing layer during its initial climb, and the conditions at the departure airport at the time were most decidedly cold if not wintry. I don't have the terminal information, but it seems it was 23 degrees F at Salt Lake City, and there were reports of light to moderate precipitation around the time of the flight, 10 am local time. If the pitot tube and/or static port iced up, could it have robbed the autopilot and/or FMS of vital airspeed and altitude information, leading to an autopilot disconnect or something like that? Or is that not possible in this type aircraft?
Again, I know virtually nothing about this type aircraft, but most of the discussion seems focused on the FMS and a possible failure, maybe an electrical one, that some suggest should not have been a real problem for an experienced pilot because of redundant electrical system components such as AC inverters and so on. Of course we shall never know all the details.
I understand that professional pilots are loathe to attribute accidents to pilot error especially when the pilot is no longer with us and is not in position to tell his side of the story, but is anything like what I suggested above at all possible?
I think I would be too scared to fly a plane like that in IMC without an additional pilot in case of an in-flight emergency, even if I had an ATP and single-pilot certification. It's like a small jet airliner, similar in complexity and performance to much larger aircraft. I think I would want some help if things got complicated. The point is, I don't think I would want to use a plane like that for personal transportation except perhaps under ideal conditions.
 
Andrew Bulgin said:
If the pitot tube and/or static port iced up, could it have robbed the autopilot and/or FMS of vital airspeed and altitude information, leading to an autopilot disconnect or something like that?
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I’m not speculating on what happened specifically here, but I have adapted this accident to the jet that I teach, and have had almost the exact same thing happen with a failure of the pilot’s static heat.

With the static ports frozen, obviously the altimeter will stop showing the climb. It’s easy enough to see that it’s happened, but the transition to copilot’s static information can cause problems...if the autopilot is still engaged, it’s still looking at pilot side pitot/static, so it’s not going to obey altitude/vertical speed commands. The normal (proper) reaction is to disengage the autopilot and hand-fly. If the pilot isn’t ready to hand-fly at that moment (not necessarily even a lack of proficiency as such, just a lack of being ready at that moment) it’s easy to fixate on a particular instrument, then be surprised by suddenly realizing that another parameter is far from where it should be resulting in over-controlling the airplane.

Along the way, the pilot’s left thumb, accustomed to trimming without conscious pilot input, does so, allowing (or causing) far greater speed, altitude, and attitude fluctuations to occur as a result of the instrument fixation, and eventually you can end up with a big enough pull at a high enough speed to cause the airplane to come apart in flight.

Again, not saying that’s what happened here, but I’ve seen that scenario develop in training. (With two ATPs in the cockpit, btw.)
 
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