Unusual Reason for an Emergency Descent

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pelmet
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Unusual Reason for an Emergency Descent

Post by pelmet » Sat Jan 05, 2019 4:43 pm

"C-FLOR, a Beech C90A King Air aircraft operated by Montair Aviation, was conducting a training flight from Red Deer (CYQF), AB to Pitt Meadows (CYPK), BC with two persons on board. During cruise flight approximately 10 nm northeast of Vancouver Harbour (CYHC), BC, the flight crew initiated an emergency descent below the minimum vectoring altitude (MVA) due to a loss of accurate airspeed indication. ATC vectored the aircraft over Indian Arm, BC to an area with a lower MVA for the aircraft to operate under Instrument Flight Rules (IFR). Upon reaching a lower altitude, the airspeed indication returned to normal. The aircraft landed without further incident at CYPK. It was determined that the pitot tube became blocked by ice."
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C-GGGQ
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Re: Unusual Reason for an Emergency Descent

Post by C-GGGQ » Sat Jan 05, 2019 5:29 pm

Would it be because of the moving Barber Pole that they felt the need as to not exceed a changeable Vne? Or is this as weird as it sounds at first glance?
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J31
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Re: Unusual Reason for an Emergency Descent

Post by J31 » Sat Jan 05, 2019 8:35 pm

If you get enough in flight icing to block the pitot tube I suspect there was a lot of airframe icing. They may not have been able to maintain altitude or needed to descend to maintain control.
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telex
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Re: Unusual Reason for an Emergency Descent

Post by telex » Sat Jan 05, 2019 11:53 pm

"Training flight" might be a consideration in this...

If you had controllability issues would you really point the thing straight down to fix it?
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Re: Unusual Reason for an Emergency Descent

Post by lownslow » Sun Jan 06, 2019 7:52 am

I have a tiny bit of time in higher-numbered King Airs but am not familiar with the 90. How many pitot tubes do 90s have? I would have thought two and both of them equipped with anti-ice capability. Is that not the case? I would hope something was lost in translation between the incident itself and the CADOR(?) being written.
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Re: Unusual Reason for an Emergency Descent

Post by C-GGGQ » Sun Jan 06, 2019 8:16 am

That's my point. Plus the article makes no mention of airframe icing, just says they lost airspeed indication. Unless the 90 is way different than the 100 or 200 first step would have been heat on not emergency decent. Either half the important info is missing or I don't know what.
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Re: Unusual Reason for an Emergency Descent

Post by C.W.E. » Sun Jan 06, 2019 10:38 am

There is probably a lot more missing.

By the way did anyone ever hear why that Navajo landed of the street in Calgary?
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Re: Unusual Reason for an Emergency Descent

Post by YYZSaabGuy » Sun Jan 06, 2019 11:50 am

C.W.E. wrote:
Sun Jan 06, 2019 10:38 am
By the way did anyone ever hear why that Navajo landed of the street in Calgary?
http://www.tsb.gc.ca/eng/rapports-repor ... 8w0054.asp
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Re: Unusual Reason for an Emergency Descent

Post by oldtimer » Sun Jan 06, 2019 4:47 pm

There is something weird going on here. A blocked pitot tube should not ever be a serious life threating malfunction. It is a malfunction true but not a true blue "killer" item. It is still possible to descend and land safely using power plus attitude. I have no time in the later model King Air C90A aircraft but in the King Air 100, 200, B200 and 350 certified for flight into known icing (the only option) and equipped with dual basic flight instruments, (again that is the way they come out of the box), all have dual heated pitot tubes, A heated pitot tube is something that is usually necessary even for a simple little single airplane that is properly equipped for night flight (moisture drain capability). All King Air airplanes that I have flown have what is usually referred to as the "hot 5", 2 pitot heat, 2 fuel vent heat and 1 stall warning vane heat and they should be turned on during line-up checks and turned off after landing. The switches are not simply a switch but rather they are switch/circuit breakers.
I have often asked other pilots (usually during training) about the emergency descent procedure they would use and they all usually say "descend rapidly to 10,000 ft"
In mountainous terrain with a MOCA well above 10,000 ft??? I cannot remember if the later model C90A King Air 90's have the stainless steel air intake lips heated by engine exhaust or do they still use the electrically heated rubber blankets.
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Re: Unusual Reason for an Emergency Descent

Post by goingnowherefast » Sun Jan 06, 2019 8:00 pm

I had a frozen pitot on a different model of King Air. It was a pretty boring malfunction. One ASI showed completely unrealistic speeds, and the other one made sense. The pilot with the normal readings took control and finished the leg.
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Re: Unusual Reason for an Emergency Descent

Post by RatherBeFlying » Sun Jan 06, 2019 8:27 pm

If the pitot ices up in cruise, the displayed airspeed will remain pretty much the same until the altitude changes; for example when it's time to descend nearing destination. Descent will lower the displayed airspeed and get the crew's attention.
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Re: Unusual Reason for an Emergency Descent

Post by iflyforpie » Sun Jan 06, 2019 8:29 pm

Maybe it was a knee-jerk attempt to get below the freezing level. Icing is scary and rightfully so—especially in a lower powered aircraft over the treacherous north shore mountains this time of year—but never at the expense of obstacle clearance unless you don’t have any other choice. Maybe they were using a terrain data base to navigate. They obviously didn’t contact anything.

I do believe the 90s have the standard five as well and most have the Raisbeck exhaust heater hot intake lips though there are still a few kicking around with the old electric ones.

Erroneous airspeed seems silly to risk a descent like that.

Attitude power trim. The plane behaves like any other even if you lose all airspeed indications.
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Re: Unusual Reason for an Emergency Descent

Post by 7ECA » Sun Jan 06, 2019 8:59 pm

Usually a good idea to give as much information as possible, when posting CADORS (but then again, pelly is looking to start a thoughtful discussion...).

CADORS number: 2017P2220

Occurrence Date: 2017-11-17

Occurrence Time: 0314 Z

After dark in November, makes it a bit more stressful - having said that it's still a bad idea to start heading down over the North Shore at night.
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Re: Unusual Reason for an Emergency Descent

Post by Heliian » Mon Jan 07, 2019 9:26 am

Sounds like they had to descend to an unpressurized altitude for the alternate static source to be used.
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Re: Unusual Reason for an Emergency Descent

Post by PostmasterGeneral » Mon Jan 07, 2019 11:07 am

Been many years since I’ve flown the thing, but in the king air wasn’t the alternate static inside the fuselage but aft of the pressure bulkhead? Meaning it wouldn’t matter if you were pressurized or not?
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Re: Unusual Reason for an Emergency Descent

Post by digits_ » Mon Jan 07, 2019 11:39 am

PostmasterGeneral wrote:
Mon Jan 07, 2019 11:07 am
Been many years since I’ve flown the thing, but in the king air wasn’t the alternate static inside the fuselage but aft of the pressure bulkhead? Meaning it wouldn’t matter if you were pressurized or not?
Isn't the alternate static source always outside the pressure cabin? Otherwise, what is the point?
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Re: Unusual Reason for an Emergency Descent

Post by Heliian » Mon Jan 07, 2019 4:07 pm

Yes, alternate is at the rear unpressurized section.

What is the procedure for use?
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Re: Unusual Reason for an Emergency Descent

Post by telex » Mon Jan 07, 2019 4:14 pm

"The alternate air source is selected by raising the clip and moving the toggle from NORMAL to ALTERNATE. The pilot's instruments then function on the alternate air source."
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Re: Unusual Reason for an Emergency Descent

Post by goingnowherefast » Tue Jan 08, 2019 8:47 am

An alternate static air source won't do much to fix a frozen pitot tube.
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