Should Have Used Pitch and Power and Ignore the Warnings

[pelmet]

Once you have unreliable airspeed, time to ignore the overspeed and stall warnings and fly known pitch and power settings. Airframe buffet remains accurate. Cruise thrust and pitch should be memorized and an early level off with an emergency declaration may be appropriate as you will have a greater margin.....

C-GBNE, a Cessna 560 Citation V operated by Keewatin Air, was conducting IFR flight KEW503
from Winnipeg/James Armstrong Richardson International Airport (CYWG), MB, to Yellowknife
Airport (CYZF), NT. Near the top of the climb at flight level (FL) 400, the flight crew observed an
ASPD annunciation and observed that the captain's primary flight display (PFD) airspeed indication
differed by approximately 25 knots from the First Officer's PFD and the electronic standby
instrument system (ESIS) airspeed indication. During troubleshooting, the aircraft indicated
conflicting airspeed and Mach indications; including repeated overspeed warnings. The engine's
thrust was reduced and the aircraft experienced an aerodynamic buffet. The flight crew
disconnected the autopilot and executed an approach to stall recovery. The flight crew declared an
emergency and requested a descent. The aircraft descended to FL290 and returned to CYWG
where the aircraft landed uneventfully.

The operator's maintenance conducted #1 and #2 pitot and static systems leak check. They
observed an excessive leak rate on the #1 pitot system and on the #2 static system. A #1 pitot
system cracked low pressure flex hose at the overspeed warning switch and the #2 static system
flex hoses at both static ports were replaced. The pitot and static systems were then tested
satisfactorily and a subsequent inspection noted that the overspeed warning switch was faulty;
which was replaced. The aircraft subsequently completed a successful test flight and was returned
to service.

....from TSB.

[CaptDukeNukem]

Once you have unreliable airspeed, time to ignore the overspeed and stall warnings and fly known pitch and power settings. Airframe buffet remains accurate. Cruise thrust and pitch should be memorized and an early level off with an emergency declaration may be appropriate as you will have a greater margin.....

C-GBNE, a Cessna 560 Citation V operated by Keewatin Air, was conducting IFR flight KEW503
from Winnipeg/James Armstrong Richardson International Airport (CYWG), MB, to Yellowknife
Airport (CYZF), NT. Near the top of the climb at flight level (FL) 400, the flight crew observed an
ASPD annunciation and observed that the captain's primary flight display (PFD) airspeed indication
differed by approximately 25 knots from the First Officer's PFD and the electronic standby
instrument system (ESIS) airspeed indication. During troubleshooting, the aircraft indicated
conflicting airspeed and Mach indications; including repeated overspeed warnings. The engine's
thrust was reduced and the aircraft experienced an aerodynamic buffet. The flight crew
disconnected the autopilot and executed an approach to stall recovery. The flight crew declared an
emergency and requested a descent. The aircraft descended to FL290 and returned to CYWG
where the aircraft landed uneventfully.

The operator's maintenance conducted #1 and #2 pitot and static systems leak check. They
observed an excessive leak rate on the #1 pitot system and on the #2 static system. A #1 pitot
system cracked low pressure flex hose at the overspeed warning switch and the #2 static system
flex hoses at both static ports were replaced. The pitot and static systems were then tested
satisfactorily and a subsequent inspection noted that the overspeed warning switch was faulty;
which was replaced. The aircraft subsequently completed a successful test flight and was returned
to service.

....from TSB.

How many air data systems on this type of airplane? 2 or 3?

Generally 1 is for captain side, two for FO side and three for backup. Most bigger jets have a fourth for AP/AT systems.

If three or more are present, you would compare to the standby and see who’s is wrong, then make appreciate decisions based on that diagnosis

[digits_]

Sounds like they did exactly that, except for the first few seconds/minutes of confusion?

It's not like you have tons of speed margin between overspeed and stall at FL400... Attitude differences between both speeds can be quite minimal, especially if you're also levelling off and your power may or may not be changing. Throw in a different load/balance, and even with your memorized attitude and power settings you might still have an interesting time...

[pelmet]

Sounds like they did exactly that, except for the first few seconds/minutes of confusion?

It's not like you have tons of speed margin between overspeed and stall at FL400... Attitude differences between both speeds can be quite minimal, especially if you're also levelling off and your power may or may not be changing. Throw in a different load/balance, and even with your memorized attitude and power settings you might still have an interesting time...

I am not sure what you mean by "exactly that" but the key statements in the report : "Near the top of the climb at flight level (FL) 400......." and "The engine's thrust was reduced and the aircraft experienced an aerodynamic buffet".

Reducing thrust in cruise at high altitude is risky. Reducing thrust while in the top end of the climb phase is worse.

A lot of people seem to be scared of an overspeed, so much so that they get themselves in a dangerous low speed situation. The aircraft has been tested for proper control above the maximum limiting speed but not below the minimum limiting speed(for obvious reasons). Don't worry too much about an overspeed and if there has to be an err......err on the high speed side.

[careerpilot?]

Sounds like they did exactly that, except for the first few seconds/minutes of confusion?

It's not like you have tons of speed margin between overspeed and stall at FL400... Attitude differences between both speeds can be quite minimal, especially if you're also levelling off and your power may or may not be changing. Throw in a different load/balance, and even with your memorized attitude and power settings you might still have an interesting time...

I am not sure what you mean by "exactly that" but the key statements in the report : "Near the top of the climb at flight level (FL) 400......." and "The engine's thrust was reduced and the aircraft experienced an aerodynamic buffet".

Reducing thrust in cruise at high altitude is risky. Reducing thrust while in the top end of the climb phase is worse.

A lot of people seem to be scared of an overspeed, so much so that they get themselves in a dangerous low speed situation. The aircraft has been tested for proper control below the maximum limiting speed but not below the minimum limiting speed(for obvious reasons). Don't worry too much about an overspeed and if there has to be an err......err on the high side.

Is it possible the autothrottle automatically reduced thrust before they could disconnect? I'm not familiar with the citation and whether it's equipped.

[Eric Janson]

Is it possible the autothrottle automatically reduced thrust before they could disconnect? I'm not familiar with the citation and whether it's equipped.

Correct. This could certainly happen if the system receives an incorrect speed input

This why on large jets the first steps after stabilising the flight path is to disconnect autopilot/autothrust and set the appropriate thrust.

[North Shore]

GBNE does not have auto thrust.

[pelmet]

GBNE does not have auto thrust.

Makes one think that thrust was manually reduced due to overspeed warnings. They had three ASI's on board. Majority rules but pitch and power wioll save the day. Should be memorized. One aircraft that I flew was typically 85% N1 and 2.5 degrees nose-up typically in cruise.