Lenbrazil From Brazil, joined Apr 2006, 114 posts, RR: 0 Posted (7 years 8 months 6 days 3 hours ago) and read 3004 times:
I'm specificlly interested in a King Air 100A if that makes a difference.
Obviously the horn can be manually tested, but how can one be sure it will sound at the right airspeed? Is it wired to the airspeed gauge? If not how does it "know" when a stall is imminent? Will it always sound at the same airspeed or would that vary depending on other factors?
(I posted the same question on the "general aviation" forum but a poster there recomended bringing it up here)
MrChips From Canada, joined Mar 2005, 923 posts, RR: 0 Reply 1, posted (7 years 8 months 6 days 3 hours ago) and read 3001 times:
The stall warning system is completely independent of the airspeed for the following reason:
An aircraft will stall if the critical angle of attack is exceeded, regardless of airspeed.
What the stall warning system does is measure the angle of attack; when it reaches a certain value, it will sound the horn. As for how to test it, there should be an angle of attack sensor on the side of the fuselage near the cockpit - it will look like a weather vane. With the aircraft power on, moving this sensor should cause the stall warning horn to go off. Of course, if the aircraft has a test function accessible from the cockpit, testing the stall warning becomes a whole lot easier.
2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 61 Reply 2, posted (7 years 8 months 6 days 3 hours ago) and read 2984 times:
AIRLINERS.NET CREW HEAD DATABASE EDITOR
Quoting MrChips (Reply 1): if the aircraft has a test function accessible from the cockpit
Not sure about the 100, but the 350 does indeed have a test function accessible from the cockpit. It's a toggle switch over on the FOs side. Holding it in the STALL WARN TEST position activates the stall warning system.
Like MrChips described, it's based on AOA. In the 350, the data comes from the lift transducer vane on the leading edge of the left wing.
2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 61 Reply 5, posted (7 years 8 months 5 days 17 hours ago) and read 2879 times:
AIRLINERS.NET CREW HEAD DATABASE EDITOR
Quoting Lenbrazil (Reply 3): OK but how could one be sure, without risking a crash, that it would give sufficient warning to prevent a stall?
Stall prevention isn't (or shouldn't be) entirely dependent upon the stall warning system. Ideally, pilots are trained to recognize other cues and conditions that lead to a stall. Mushy controls/reduction in control effectiveness, nose-high attitude, buffeting (not the Jimmy kind), vibrations, etc, should all alert the pilot to an impending stall as effectively as the stall warning system itself.
AvionicMech From United Kingdom, joined Jan 2005, 315 posts, RR: 3 Reply 8, posted (7 years 8 months 5 days 16 hours ago) and read 2850 times:
The stall warning system will be checked if the aircraft is having a test flight after maintenance or for the authorities. But this will not involve actually stalling the aircraft but just activating the system then the aircraft will be accelerated out of it. The airspeed at which the stall warning system activated will be noted and compared to a figure calculated from the aircraft weight and altitude. This would normally be conducted at an altitude of around 10,000ft so that a safe recovery could be performed should the aircraft actually stall.
WrenchBender From Canada, joined Feb 2004, 1779 posts, RR: 9 Reply 12, posted (7 years 8 months 5 days 11 hours ago) and read 2784 times:
at 8500 Lbs, full flap, no bank @48 KIAS.
(I know the Twotter is not renowned for its speed or high performance but you'll get there in the end)
Here is the quote from the Flight Test:
'Conduct power-off stalls with flap settings of 0, 10 and Full. Approach the stalls at an airspeed bleed rate of not exceeding one knot per second (it is not necessary to maintain level flight for this test). Record the stall warning and stall airspeeds. The stall warning light should illuminate 4 to 9 knots above the stall airspeed.'
Lenbrazil From Brazil, joined Apr 2006, 114 posts, RR: 0 Reply 13, posted (7 years 8 months 5 days 11 hours ago) and read 2775 times:
Quoting 2H4 (Reply 5): Stall prevention isn't (or shouldn't be) entirely dependent upon the stall warning system. Ideally, pilots are trained to recognize other cues and conditions that lead to a stall. Mushy controls/reduction in control effectiveness, nose-high attitude, buffeting (not the Jimmy kind), vibrations, etc, should all alert the pilot to an impending stall as effectively as the stall warning system itself.
I'd hope so to but in the case of the crash I'm looking into (no survivors, no black boxes, no distress call) the pilot was known to be a screw-up and distractable.
Sfomb67 From United States of America, joined Dec 2005, 417 posts, RR: 0 Reply 15, posted (7 years 8 months 5 days 10 hours ago) and read 2756 times:
Quoting AvionicMech (Reply 8): The stall warning system will be checked if the aircraft is having a test flight after maintenance or for the authorities. But this will not involve actually stalling the aircraft but just activating the system then the aircraft will be accelerated out of it
I've been on several test flights on DC-8 & 762's out of HMV as an observer, and I believe the acft was either stalled, or on the edge of stalling, in order to test the stick shaker/stall warning sys. at a precalculated speed. As it was quoted above, "then the aircraft will be accelerated out of it."
Fly727 From Mexico, joined Jul 2003, 1789 posts, RR: 19 Reply 17, posted (7 years 8 months 5 days 10 hours ago) and read 2747 times:
Can Stall Alarms Be Tested And If So How?
Most of the airliners have a stall test switch but all have pointed that out. My input here is about General Aviation airplanes, such as those from the Cessna family. On some of them, to test the alarm you would have to literally suck air from it and hear it sound. Good practice was to make sure no dirt or bugs were in the alarm area or you could get a free, unexpected -and sometimes crunchy- snack.
Or... you could do it the right way according to the following Airworthiness Directive:
"To assure proper operation of the stall warning system accomplish the following:
(a) Prior to flight, test the pneumatic stall warning system and determine if it is functioning properly... ....which tells operators to test the horn operation by covering the opening in the left wing with a clean cloth, such as a handkerchief, and applying a slight suction by mouth to draw air through the horn. A properly functioning horn will provide a sound that is clearly audible. The check required by this part of the Airworthiness Directive maybe (sic) performed by the pilot."
There are no stupid questions... just stupid people!
Mir From United States of America, joined Jan 2004, 20509 posts, RR: 56 Reply 18, posted (7 years 8 months 5 days 8 hours ago) and read 2727 times:
Quoting Lenbrazil (Reply 14): How unusual is it for alarms to be found to activate too late?
Are there conditions under which the alarm might activate too late during a "real" flight?
The stall warning horn will always go off before the stall - it's physically designed to do so. Whether that is too late is another story - though I would say that as long as the plane isn't upside down or on its side, you should have enough time to firewall the throttles, push the yoke down, and fly out of the impending stall if you react right away.
7 billion, one nation, imagination...it's a beautiful day
FlyGaz From United Kingdom, joined Nov 2004, 70 posts, RR: 0 Reply 19, posted (7 years 8 months 5 days 8 hours ago) and read 2717 times:
In some general aviation aircraft there is the possibility that conditions may exist so that the stall warning horn may not sound. For example, in the PA 38 Piper Tomahawk I fly, if the electrical system fails during flight, the stall warning horn also stops sounding (because it is linked to the electrical system).
Because of this we learn early on in training to recognise the symptoms before the stall occurs, such as buffeting and sluggish controls. So if something happens to prevent the stall warner activating, the pilot should be able to still prevent a stall.
I'd hope so to but in the case of the crash I'm looking into (no survivors, no black boxes, no distress call) the pilot was known to be a screw-up and distractable.
I would be careful saying something like that - a statement like that makes it sound like you've already drawn your own conclusions in the absence of proper evidence.
The case I'm refering to is the Wellstone crash; the short comings of both pilots were well documented.
Richard Conry the PIC normally let his co-pilots fly. 2 of them said they had to take the controls away from him because he couldn't maintain altitude. Even when he wasn't the PF he was a hazard -just 2 days before the crash his SIC was taking off in another King Air and he accidentally activated the autopilot instead of the yaw damper. The plane was only 300 feet off the ground and it pitched sharply downward, the situation was corrected by the co-pilot who said Conry was oblivious to what had gone wrong. After the flight the co-pilot suggested Conry retire. There were was a report of an incident when he almost took out a control tower on take off. These incidents (and there are more) all happened during the 17 month period he worked for Aviation Charter, during which accumulated only 600 hours. Only a few months before the crash he told a close friend he had difficulty flying King Airs esp during take off and landing. he probably wasn't wearing contact lenses as mandated by the FAA.
As for the co-pilot, Michael Guess, he had been fired from both his previous piloting jobs for incompetence. There were also several reports of his weakness as a pilot esp. during take off and landing. Conry told his wife the other pilots at Aviation Charter thought Guess was a poor pilot.
WrenchBender From Canada, joined Feb 2004, 1779 posts, RR: 9 Reply 24, posted (7 years 8 months 4 days 3 hours ago) and read 2532 times:
Quoting 2H4 (Reply 20): Oh, I didn't mean to discredit the Twotter in any way. I love those things, and have always wanted to fly one.
Don't worry, it's a love hate relationship. VNE on the Twott is 171 KIAS, that's the same as some helicopters. We once had to stop for gas in Regina enroute to Cold Lake from Winnipeg (the trucks below us on the highway were travelling faster). If your on ski's or floats it's even worse. But you can get into anywhere with the Twott, not many other aircraft are as versatile.
2.10 Low-Airspeed Alert Systems
Current Federal airworthiness standards require that airplanes be equipped to provide a clear and distinctive stall warning to the flight crew at a speed that is at least 5 knots higher than stall speed. However, stall warnings do not always provide flight crews with timely notification of developing hazardous low-airspeed conditions. For example, abrupt maneuvering can increase angle-of-attack so rapidly that a stall could occur nearly simultaneously with the stall warning, and ice accumulation, which raises the stall speed, could degrade the stall warning margin to the point at which little or no stall warning is provided.
The accident airplane was equipped with a stall warning system designed to sound a horn in the cockpit 5 to 8 knots before the actual stall speed of the airplane in any configuration. However, as discussed previously, because the airplane was not equipped with a CVR, because of the approximate nature of the airspeed calculations, and because abrupt airplane maneuvering or even small amounts of ice accumulation can defeat the airplane.s stall warning system, the Safety Board was not able to determine when or if the stall warning horn activated before the onset of the stall. Regardless of when or whether the stall warning horn activated, it is clear that the accident flight crew failed to maintain airspeed during the approach. As discussed in section 2.3, radar data indicate that the accident flight was operated below Aviation Charter.s recommended approach speed for about the last 50 seconds of the flight.
The Safety Board has investigated numerous accidents and incidents involving commercial flight crews that inadvertently failed to maintain adequate airspeed. For example, the Board has investigated at least 11 events since 1982 involving Part 135 flights and at least 7 events involving Part 121 flights in which stall or failure to maintain airspeed during the approach or landing phases was cited as a causal or contributing factor and in which icing was not cited as a factor. In addition, the Board has investigated other events in which the drag associated with airframe ice and pilot inattention led to a critical loss of airspeed. Failure to maintain airspeed during these flights resulted in catastrophic and other unsafe circumstances, such as loss of control, impact with terrain or water, hard landings, and tail strikes.
A 1996 FAA Human Factors Team86 Report titled, .The Interfaces Between Flight Crews and Modern Flight Deck Systems,. expressed concern about the history of accidents involving lack of low-airspeed awareness in the context of flight crews monitoring automated systems. This report states the following:
“flight crews may not be provided adequate awareness of airplane energy state, particularly when approaching or trending toward a low energy state.Transport category airplanes are required to have adequate warnings of an impending stall, but at this point the airplane may already be in a potentially hazardous low energy state. Better awareness is needed of energy state trends such that flight crews are alerted prior to reaching a potentially hazardous low energy state.”87
This accident history was also cited by the Flight Guidance System Harmonization Working Group of the Aviation Rulemaking Advisory Committee (ARAC), when, in March 2002, it proposed revisions to FAR 25.1329 and AC 25.132988 to provide low-airspeed protection and alerting during autopilot operations for newly certified transport-category airplanes. The proposed regulatory revision would require, .[w]hen the flight guidance system [FGS] is in use, a means ‘to avoid excursions beyond an acceptable margin from the speed range of the normal flight envelope’. The proposed new AC, which is intended to provide an acceptable means for showing compliance with this new requirement, states the following:
The requirement for speed protection is based on the premise that reliance on flight crew attentiveness to airspeed indications, alone, during FGS.operation is not adequate to avoid unacceptable speed excursions outside the speed range of the normal flight envelope..Standard stall warning and high speed alerts are not always timely enough for the flight crew to intervene to prevent unacceptable speed excursions during FGS operation..A low speed alert and a transition to the speed protection mode at approximately 1.2 Vs,  or an equivalent speed defined in terms of Vsr,  for the landing flap configuration has been found to be acceptable.
The proposed changes to FAR 25.1329 reflect the advanced avionics capabilitiescharacteristic of modern transport-category airplanes. However, the Safety Board notes that a low-airspeed alert system has been developed for Embraer EMB-120 airplanes; installation of the alert system was mandated by FAA Airworthiness Directive 2001-20-17.91 The system is designed to alert flight crews of low-airspeed conditions in certain airplane configurations and in icing conditions through the use of an amber-colored indicator light installed in the control panel and an audible alert. The Board is also aware that several avionics manufacturers offer low-airspeed alert devices associated with approach and maneuvering speeds for use in less sophisticated general aviation airplanes. This demonstrates that it may be feasible to develop low-airspeed alert systems for most airplane types.
2.10.2 Need for Improved Low-Airspeed Awareness
The Safety Board recognizes that the development and requirement of a low-airspeed alert system is a departure from the previously accepted premise that adequate low-airspeed awareness is provided by flight crew vigilance and existing stall warnings. However, the circumstances of this accident and the history of accidents involving flight crew lack of low-airspeed awareness suggest that flight crew vigilance and existing stall warnings are inadequate to reliably prevent hazardous low-airspeed situations and that this unsafe condition is not unique to autopilot operations or flight in icing conditions. If a low-airspeed alert system had been installed on the accident airplane, it might have directed the attention of the flight crew to the airplane.s decaying airspeed in time for them to initiate appropriate corrective action. For example, if a low-airspeed alert had activated when the airspeed dropped below 1.2 Vs (about 92 knots for the accident airplane), the flight crew would have received about 15 seconds advance notice before reaching the airplane.s estimated stall speed. In addition, if the flight crew had maintained an airspeed at or above the threshold set by such an early low-airspeed alert, the additional airspeed could have prevented an accelerated stall initiated by an abrupt last-second maneuver or provided an improved speed margin above a premature stall caused by ice accumulation on the wings.
This change in philosophy is evident in the ARAC.s proposed changes to FAR 25.1329 and AC 25.1329, Embraer.s requirement for a low-airspeed alert system on the EMB-120, and the fact that several avionics manufacturers offer low-airspeed alert devices for general aviation airplanes. The Safety Board supports this change in philosophy. A low-airspeed alert associated with the minimum operationally acceptable speed for a particular phase of flight would likely help flight crews maintain airspeed awareness in much the same way that altitude alert systems help flight crews maintain altitude awareness. Enhanced airspeed awareness would also likely provide an additional safety margin against stall and loss of control events at low altitudes where recovery is difficult, as was the case in this accident.
The Safety Board recognizes that there are unresolved technical, operational, and human factors issues that will need to be carefully evaluated and addressed in connection with the design and implementation of a low-airspeed alert system.92 The Board encourages the FAA to consult with representatives from NASA and other aviation industry specialists in resolving and addressing these issues. Despite these unresolved issues, the Safety Board concludes that the development of and requirement for the installation of low-airspeed alert systems could substantially reduce the number of accidents and incidents involving flight crew failure to maintain airspeed. Therefore, the Safety Board believes that the FAA should convene a panel of aircraft design, aviation operations, and aviation human factors specialists, including representatives from NASA, to determine whether a requirement for the installation of low-airspeed alert systems in airplanes engaged in commercial operations under 14 CFR Parts 121 and 135 would be feasible, and submit a report of the panel.s findings. The Safety Board further recommends that if the requested panel determines that a requirement for the installation of low-airspeed alert systems in airplanes engaged in commercial operations under 14 CFR Parts 121 and 135 is feasible, the FAA should establish requirements for low-airspeed alert systems, based on the findings of this panel.
86 This team comprised FAA and industry representatives.
87 Federal Aviation Administration, Human Factors Team Report, The Interfaces Between Flightcrews and Modern Flight Deck Systems (Washington, DC: FAA, 1996).
88 Similar changes were also proposed to Joint Aviation Requirements (JAR) 25.1329 and Advisory Circular Joint 25.1329. The FAR/JAR and ACs are currently titled, .Automatic Pilot System.; the proposed new titles would be .Flight Guidance System..
89 Vs is the stall speed or the minimum steady flight speed at which the airplane is controllable.
90 Vsr is the reference stall speed.
91 This low-airspeed alert system was developed as a result of the January 9, 1997, accident involving Comair flight 3272, an EMB-120RT that crashed near Monroe, Michigan, during a rapid descent after an uncommanded roll excursion in icing conditions and the March 19, 2001, accident involving Comair flight 5054, an EMB-120 that departed controlled cruise flight and descended 10,000 feet after it encountered icing conditions.
92 Some of the issues that should be addressed include the following: defining the target speed at which the alert system would activate, effectively integrating such a system with other aircraft systems, preventing nuisance alarms and flight crew over-reliance on such a system (see, for example, A.R. Pritchett, .Reviewing the Role of Cockpit Alerting Systems,. Human Factors and Aerospace Safety Vol. No. 1 : 5-38), differentiating such an alert from other kinds of cockpit alerts and warnings, and developing flight crew procedures on and training for the use of such systems.