Colgan DHC-8 crashed in Buffalo

[scottkin]

Greetings!

Again I can only speak for the aircraft I fly, but here is a general overview of the normal vertical modes for the flight director (and autopilot if it is turned on) in the CRJ.

Vertical speed mode captures a rate of climb or descent and adjusts the pitch of the command bars on the ADI (attitude indicator) to maintain it.

Speed mode captures a speed and adjusts the command bars to maintain it. This can also be changed to climb or des mode where the plane will keep a minimum of 200fpm in the direction that you choose. For our airplane at my airline this mode is not allowed to be used during an approach.

Glideslope mode captures the glideslope that is present during an ILS approach and will adjust the pitch of the aircraft to maintain it.

Pitch mode will simply hold a certain pitch attitude. It is a pretty primitive mode and I have seldom seen anyone who uses it.

So to answer your question, vertical speed mode is what most people use to descend to which ATC clears us to before starting the approach. On an ILS (whether hand flown or coupled to the autopilot) approach mode will arm once you have selected it and the localizer comes "alive". Once you are established on the localizer and intercept the glideslope the glideslope mode will become active and now the command bars will give you pitch commands to remain established.

Hope this is what you were looking for.

Perfect..Thanks again. I will be very curious to see what comes out about what mode the pilot was in before autopilot was disconnected. I posted a link earlier in the thread about an incident that was very similar to this one except they were ascending. Fortunately for them they had a little more altitude to play with and recovered. Also, they wern't in a flat spin. I hope this one is solved quickly.

[AVION1]

Anyone familiar with the "sheer pins" located at the Autopilot Servoes?..
I have been thinking about the possibility that something went wrong and they never broke lose from the servoes and the gears, turning the aircraft really difficult to fly....is like trying to fly a "typewriter machine"...

[AVION1]

Probably not a professional one though.

from Spartan School of Aeronautics with an A/S in AMT...AMEL/Instruments and A&P, and a Repairman Certificate for the Repair Station I am working as Avionics Chief Inspector. Any more questions?

[Dmmoore]

This was published by AVWEB today, Monday 16 Feb. http://www.avweb.com/eletter/archives/avflash/1316-full.html Top News: Latest Details on Buffalo Crash back to top Q400 Pitched Up 31 Degrees Before Crash Click for larger image The crew of the Bombardier Q400 that crashed in Buffalo on Thursday got a stall warning and the stick pusher engaged but still the aircraft pitched upward 31 degrees before turning almost 180 degrees and dropping onto a house in the Buffalo suburb of Clarence Center, near the outer marker for Buffalo Niagara International Airport. The sequence of events, which included a 45-degree dive with a 106-degree right bank ended 26 seconds later in the fireball on the ground, killing 49 people on the plane and one on the ground, the owner of the house. Although icing continues as a theme in the investigation, reporters were told at an NTSB press briefing on Sunday that the aircraft's anti-icing system had been on for most of the flight and, while both pilots discussed the "significant" icing their aircraft was experiencing, at no time did they use the "severe icing" descriptor that is the official notification of flight-threatening buildup. "We don't know that it was severe icing," NTSB member Steve Chealander told reporters. "They [the crew] didn't say that it was severe icing....The weatherman didn't say that it was severe icing." Initial reports suggested the aircraft, flying as Continental Connection Flight 3407 dove on the house but later reports said it crashed in a flat attitude. According to data released at the press conference, the last radar hit showed the aircraft with a forward speed of only 100 knots and it lost 800 feet in five seconds. The autopilot was on for part of the sequence and the engines were set to full power just before impact.

It appears more is involved than simple icing and a tail stall.

[Falconer]

Anyone familiar with the "sheer pins" located at the Autopilot Servoes?..
I have been thinking about the possibility that something went wrong and they never broke lose from the servoes and the gears, turning the aircraft really difficult to fly....is like trying to fly a "typewriter machine"...

PD: The sheer pins are supposed to break in case the A/P doesn't disengage by itself..

Actually it's shear pins. But what normally happens is that the autopilot servos, at least in the aircraft I have flown have clutches that have a specific point at which they disengage. Nothing breaks, they just turn the airplane loose. At least one aircraft that I'm rated in has that as part of the preflight autopilot test,where you manually override the autopilot and confirm that it indeed does disengage. Many autopilots have either indicators in the cockpit or warnings that advise the crew that the autopilot is being overworked. Lights like "aileron mistrim" "elevator mistrim" or "trim right(left) wing down" are pretty common.

[atco]

Something that has struck me as unusual looking back over the things we know so far.

At the time of the incident, when the aircraft was established inbound in a flap 5, gear down configuration, was the it was only flying at 134kts.

Now given that the crew had selected the +20kts reference speed switch that would seem awfully slow to me 5~6 miles from touchdown.

Bearinf in mind that BUF is not as busy as larger airports, but most airport arrival sequences usually involve a 160kt speed restriction to the marker. I know here at YYZ we use 160kts in IMC and 170kts in VMC. One of the benefits of this restriction is that the tower knows exactly what speed the inbound aircraft is at in oder to guage its departure intervals.

Now with the +20 switch enacted that would mean that at 134kts, the aircraft would otherwise have been at 114kts, again this just seems too slow that far out.

I saw some figures on pprune that suggested for the approx landing weight (which i assume would be a guess - not sure if it was from a DH8D pilot or not) that the aircraft should have been at approx 164kts with the +20 switch engaged. At that distance from the runway that seems to be a more logical speed.

Whats interesting though is that even at 134kts, it seems the autopilot was not constantly trimming the aircraft as one would expect if it was about to enter a stalled condition.

[LiaNY]

Is it possible that wind shear was involved since the plane took such a big drop in altitude so fast? Forgive me if I am way off base but I am not a pilot.

[scottkin]

Is it possible that wind shear was involved since the plane took such a big drop in altitude so fast? Forgive me if I am way off base but I am not a pilot.

Just an educated quess here Lia. The reason it dropped so fast because the airplane stalled. Like dropping a brick off a 20 story building.

[AVION1]

Now with the +20 switch enacted that would mean that at 134kts...
SORRY, I AM NOT FAMILIAR WITH THAT SWITCH.
IS THAT SWITCH SOMETHING LIKE AN ALCOHOL-WATER POWER BOOSTER INJECTED IN THE COMBUSTION CANS?
I REMEMBER THE METROLINER HAS THIS FEATURE !! YOU CAN GET ABOUT 20% MORE POWER OR TORQUE..SPECIALLY IF YOU ARE IN TROUBLE.

[T.O.G.A.]

I have read all of the previous posts. Perhaps too quickly to know if my question has been answered. If the deicer boots were on for the majority of the flight, How would the aerodynamics of the wing or H-stab be changed by ice if the deicer boots were functioning?

I read one post that said it is possible that ice built up behind the boots but that would be a serious issue wouldn't it? One that would have caused other accidents in the past and since corrected?

[Falconer]

Now with the +20 switch enacted that would mean that at 134kts...
SORRY, I AM NOT FAMILIAR WITH THAT SWITCH.
IS THAT SWITCH SOMETHING LIKE AN ALCOHOL-WATER POWER BOOSTER INJECTED IN THE COMBUSTION CANS?
I REMEMBER THE METROLINER HAS THIS FEATURE !! YOU CAN GET ABOUT 20% MORE POWER OR TORQUE..SPECIALLY IF YOU ARE IN TROUBLE.

It has nothing to do with increased power.

[LiaNY]

Just an educated quess here Lia. The reason it dropped so fast because the airplane stalled. Like dropping a brick off a 20 story building.

I have read about the stalling but would a stall cause an aircraft to drop that fast?

On a related note, I have flown in many turbo props when we had to land or take off in thunderstorms...or remained in the clouds in thunderstorms while in a holding pattern. The pilots would always come on and explain that it might be bumpy (and sometimes it was) but it was never so bad that I thought I was going to die.

The worst turbulence I experienced was in clear, perfect sunny weather flying over the mountains on a Seattle to NYC flight.

[screaming_emu]

from Spartan School of Aeronautics with an A/S in AMT...AMEL/Instruments and A&P, and a Repairman Certificate for the Repair Station I am working as Avionics Chief Inspector. Any more questions?

University of North Dakota with a BS in Commercial aviation and I have an radio operators certificate....

now that doesn't make me qualified as a professional avionics chief inspector, does it?

[MichaelWSmith]

The Digital Fight Data Recorder (DFDR) in modern aircraft like this record continuously, I believe somewhere around 200+ individual parameters.

Atco and AVION1, thanks for answering my question about the FDR.

[Airbus_A320]

I have read about the stalling but would a stall cause an aircraft to drop that fast?

On a related note, I have flown in many turbo props when we had to land or take off in thunderstorms...or remained in the clouds in thunderstorms while in a holding pattern. The pilots would always come on and explain that it might be bumpy (and sometimes it was) but it was never so bad that I thought I was going to die.

The worst turbulence I experienced was in clear, perfect sunny weather flying over the mountains on a Seattle to NYC flight.

When an aircraft stalls, it means that the wings are no longer producing lift, therefore the plane starts dropping. What you experienced in perfectly sunny weather is known as clear air turbulence. Thunderstorms, and warm weather in general produce a lot of updrafts which cause turbulence. While turbulence is annoying and uncomfortable, it alone isn't going to harm the airplane.