The indicated speed at which a particular aircraft operating at a particular total weight will stall when in straight and level flight at a given air density which broadly corresponds to altitude will not be very different for the climb and descent case at that air density — but it will increase as bank angle increases since in a turn, the lift from the wing must exceed the weight being supported.
As air density decreases with increasing altitude, more lift must be generated by an aerofoil to sustain flight and so the true air speed at which an aerofoil will stall will increase.
However, this fact is not of direct relevance to the pilot since the airspeed displayed is indicated air speed derived from the ambient air density. Thus, the indicated speed at which an aircraft will stall will be the same at any altitude.
On a propeller driven aircraft with engines ahead of the wing, the slipstream from each engine can change the angle of attack for the area of the wing that it affects, when compared with the angle of attack of those parts of the wing in the free airflow. Thus the wing will stall in parts, not all at once. Therefore, the power set, and the resulting slipstream effects, will change the speed at which stalling becomes apparent in any particular configuration.
On all transport aircraft, some form of stall protection system is a certification requirement. If they now rely on the defective sensor, this quickly leads to disaster. Read more: US demands Boeing make changes to Max 8. In three flight accidents in recent decades, a faulty speed measurement with a so-called Pitot tube was the cause of the crash: Birgenair flight crashed in during the climb in the Dominican Republic.
Dust had probably accumulated in the speed measuring tube. A very similar cause was found in the crash of Aeroperu flight in the same year. Only the tube was not dirty there, but taped up as a precaution. The problem was, nobody had removed the tapes before the start. In both cases the Pitot tube signaled to the pilots a speed that was much too high. In the case of the Birgenair flight, the pilot tried to counteract this by pulling up the nose of the aircraft - a devastating mistake.
The pilot ignored the correct data from a second sensor and a warning signal about the impending stall because he was probably confused and overwhelmed by the wrong speed information.
Read more: Boeing MAX: a plane of compromise. Indonesia's chief investigator Nurcahyo Utomo explains the events, that led to the Lion Air crash in During the Aeroperu flight, the crew was able to initiate a landing manoeuvre. During the landing attempt it stalled and then crashed. During Air France flight in the Pitot tube probably iced up.
However, here the aircraft was already at cruising altitude. When the autopilot then switched off, the pilots were probably distracted by an abrupt tilting of the aircraft and tried to bring the jet back under control by pulling the plane up too steeply. So they also caused a stall, which led to a crash over the Atlantic. Aircraft manufacturers are trying to deal with the known danger in two ways: On the one hand, pilots are specifically trained to cope with erroneous measurement data from sensors and to interpret them correctly despite confusion and possible panic.
On the other hand, the technology should improve and also intervene when stressed pilots make the wrong decisions. Boeing has introduced a "Maneuvering Characteristics Augmentation System" MCAS for the Max models, which can detect critical flight situations and intervene in the event of an imminent stall, but only when the autopilot is switched off.
This can be the case, for example, shortly after take-off during ascent, but also when sensors provide unreliable measurement data - as was the case with the Air France flight. Here it was apparently not the Pitot tubes that were faulty, but the sensors that determine the angle of attack of the wings. The two sensors deviated from each other by up to 20 degrees.
This accident also occurred shortly after take-off during the critical climb phase. Although the investigation has not yet been completed, there are some indications that the MCAS tried again and again to initiate a descent before the crash, while the pilot tried 26 times to raise the nose of the aircraft again.
Also in the crash of Ethiopian Airlines flight on March 10, , there is at least an indication of a connection to the MCAS system. The flight monitoring service "Flightradar 24" registers an "unstable vertical speed". This could mean that pilots and robots may have worked against each other. But there will be clarity at the earliest when the flight recorders have been found and evaluated. This picture shows why the Boeing aircraft officially designated the was quickly given the nickname "jumbo jet" shortly after its market launch 50 years ago.
The four-engine jet is simply huge. The two had a long-standing friendship. According to legend, Trippe is said to have approached Allen as the plane-maker was finishing plans for the wide-body aircraft: "If you build it, I'll buy it. As the nose will want to yaw and pitch down, keep straight with rudder and hold the altitude with increasing backpressure on the control column.
The first true symptom is a decreasing airspeed. Low airspeed and a high nose attitude are not always present in the approach to the stall. For example, the high-speed stall as a result of pulling out of a dive too sharply. Therefore, although it is desirable to inform the student that a high nose attitude and low airspeed are indicators of an approaching stall for most phases of flight, they will not always be present.
The next symptom is less effective controls as a result of the lowering airspeed — as they will have experienced in the Slow flight lesson. The student should also recognise the progressively increasing stick forces as the stall is approached. Reduced control effectiveness is usually followed by the stall-warning device. However, this is not a true symptom, as the device is mechanical and may not work. The type and operation of the stall-warning device fitted to the aeroplane should be described.
The last generally noted symptom is the buffet. This is caused by the turbulent airflow from the wings striking the empennage. This is because the airflow breaking off the high wing combined with the high nose attitude, results in most of the turbulent airflow missing the empennage.
At this point, as a result of the low airspeed, elevator effectiveness has been reduced to the point where no further increase in angle of attack can be achieved, even though the control column is held well or fully back. This results in the aeroplane sinking and the change in relative airflow causes the critical angle to be exceeded. The aeroplane stalls, altitude decreases and generally the nose pitches down.
It is important the student be able to correctly identify when the aeroplane has stalled. The recovery is broken down into two distinct parts: unstalling the aeroplane, and minimising the altitude loss. To unstall the aeroplane , the angle of attack must be reduced. Since increasing the backpressure or pulling back increased the angle of attack, decrease the backpressure or check forward. In addition, no aileron should be used; ailerons must be held centralised, for reasons that will be discussed in the briefing Advanced stalling.
However, the correct use of aileron must be stated right from the beginning in order to get the sequence right first time and every subsequent time. You should be attempting to introduce stalling in its simplest and most basic form. Therefore, every effort should be made to avoid the wing-drop. If the aeroplane has a known tendency to wing-drop in the basic configuration it may be necessary to explain this tendency and the result, as well as the reason for not using aileron in the recovery refer CFI.
If an explanation is required, keep it as simple as possible at this level. Your choice of terms — check forward, relax backpressure, ailerons neutral, no aileron, or ailerons central — should match your airborne patter.
It should be made clear that reducing the angle of attack is all that is needed to unstall the aeroplane. The aeroplane will enter a descent, and the student can now regain straight and level from the descent PAT.
The altitude loss will be about feet using this method, and will be the first recovery method the student practises. For the least loss of altitude, the maximum amount of power is required hence carburettor heat COLD during the entry so smoothly but positively apply full power prevent yaw — keep straight and raise the nose smoothly to the horizon.
There is no need to hold the nose down, as excessive altitude will be lost. Similarly increasing backpressure too rapidly, or jerking, may cause a secondary stall. Nose-on-the-horizon may be used as the reference attitude. Of the attitudes the student is familiar with the level attitude is too low and the aeroplane will continue to sink, resulting in unnecessary altitude loss. Alternatively, the climb attitude is too high, as the pitch-up created by full power combined with inertia may result in a secondary stall.
A compromise attitude is required to arrest the sink and allow the aeroplane to accelerate to the nominated climb speed. The simplest attitude to use is to put the top of the nose cowling just on the horizon. For some light aeroplanes this attitude is the same or similar to the climb attitude, but at least the student has not been encouraged to try to climb by simply pointing the aeroplane upwards. The aeroplane should be held in the nose-on-the-horizon attitude until the nominated climb speed is reached and then the climb attitude selected.
Common practice is to use the recommended or normal climb speed, for example 70 knots. However, you may nominate speed for best angle of climb or for best rate of climb refer CFI. Straight and level flight should be resumed at the starting altitude and the reference point or heading regained if necessary. All stalling exercises should finish with a recovery at the incipient stage, more commonly referred to as the onset.
This is to emphasise that, under normal conditions of flight, the stall is avoided. The second objective of this exercise is to recover at onset, which means at the stall warning or buffet.
The stall itself is simply the stall and is sometimes referred to as fully developed, meaning that the stall has occurred. A fully developed stall does not imply a wing-drop. The expected altitude loss from a recovery at onset depending on which symptom is first detected should be stated, for example, less than 50 feet.
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