L39Guy wrote: ↑Wed May 22, 2019 12:13 am
The big difference between Aeroperu and the MAX situation is that there was no UAS drill prior to Aeroperu but there is one for the MAX. A UAS drill was one of the lessons learned from Aeroperu.
You brought up a very interesting point. It took 70 years of commercial flying before Boeing decided that an UAS drill was required ?
What made that change necessary ?
In basic aircraft design, an aircraft instrument panel is made to be redundant and there is always a backup system that allows you to survive in case of loss of any one system. A basic Cessna 172's panel has :
The magnetic compass (self contained)
An Airspeed Indicator (pitot tube and static port)
A Vertical Speed Indicator (static port)
A Directional gyro (Vacuum pump)
An Artificial Horizon (Vacuum Pump)
A Turn and Bank Indicator or a Turn Coordinator (Electrical)
A Stall warning (self contained)
The loss of either the Vaccum Pump, the electrical system, the pitot tube or the the static port will still leave enough instruments working to keep control of the aircraft. Pilots are taught very early to not only know what system powers what instrument but also to know which instruments they can trust and which they must remove from their scan once the failed system has been identified.
This was still true in early transport Category aircraft, even when the systems got more complex. The electrical systems for example became more complex and buses were introduced with electrical back ups. Some instruments needed an inverter to work on AC, while others were DC. Still pilots were taught which was which and knew exactly what instruments failed when a generator or an inverter was lost, and which ones remained operational.
This segregation was however lost at a certain stage of aircraft design. Today, in glass cockpits, all instruments are electrical, so a total loss of electricity would spell disaster. The electrical system became complex, so the failure of one instrument powered by one bus would not knock out the whole system. There are AC and DC buses, main buses, emergency buses, battery buses, bus ties etc.
But we still have as instrument sources the classic pitot tubes, static ports and AOA vanes. There are also new input sources such as IRS And GPS. When today's pilot looks at his instrument panel, can he really know with certainty which will work and which will not in the advent of the loss of a particular system ?
On the 737 NG, the loss of of the AOA probe affects the Indicated airspeed. Huh ?
In the Airbus 330, the VSI is hybrid Static-Port and IRS. Huh ?
In the Airbus 330, in case of unreliable airspeed, we are told to always trust the stall warning indication which is independent of the Pitot Static (like in most aircraft).
In the Boeing 737NG, we are told on the contrary NOT to trust the stall or over-speed warnings in case of and unreliable airspeed.
Now, because of the complexity of the aircraft systems and the way they are programmed into the aircraft software, we have failures of some systems which cause erroneous indications of other systems that at first impression are totally foreign to the failed system.
The AeroPeru 757 had one problem and one problem only. Clear scotch tape had been applied to all its static ports by those who had been tasked with cleaning the aircraft had installed to avoid spaying water in them after they had been asked to wash the aircraft and warned not to spray water in the static ports. They forgot to remove the tape, and the flight crew who did the walk around at night, failed to see the clear scotch tape over all the static ports.
What should have been a clear case of a pitot-static problem had this jet been an older 737 or DC-8, turned into a nightmare for the 20,000 hour captain because of the conflicting and multiple unrelated warnings he experienced after take off.
Airspeed Indication Problem
VSI indication problem
Wind shear warning
Rudder Ratio Warning
MAch TRim Warning
This is what happened to AeroPeru
This is what happened to Air France 447
I don't blame the 737 MAX pilots one bit for their failure to save the aircraft.