Hi,
Machinbird:
Actually a good "Redundant Design" can support (degrading) even major failures.
Our human body is an example: We are adequately redundant: Duplicated lungs, Kidneys, arms, etc. The Designer (
implemented this SAFETY feature extensively in nature.
The "Fault Tolerance and Graceful Degradation" was certainly the major achievement of this "Design Approach", actually by " Species Evolution".
On big Systems we may comment Fukushima disaster on that:
Their "APU" failed completely (when they most needed it) after the "protections" were triggered (by the G's) and the ABSOLUTELY NECESSARY cooling of the reactors ceased what lead to a "Thermal Runway".
They had to use Chinooks (risking) during subsequent days at the emergency peak of the event.
Why it failed? The March 11 wave was taller (than the expected maximum). The "equipt" operated as per design.
. Like the 747 cargo door issue (flt 811) and a multitude of other sad examples.
The Engineers responsibility is enormous: Quality (the result of the design) depends totally from a good Specification.
In aviation, as many here commented the pilot must operate "inside" the "machine limits". Example: The Pitot's current limitations. The first threat F-GZCP "received" was the path (with a "last minute" slight deviation) towards a WX other crews deviated. This exceeded the limits of an important element of the System, (Pitot's) triggering a cascade of events. A rare chain so complex, being regarded as directly related to (complex and "subjective") Human Factors.
The Redundancy applied in modern airliners is carefully studied to the Industry requirements.
And frequently reduce the consequences (after major failures) or even transform potential serious accidents in "manageable incidents".
It can tolerate major failures? Examples abound. And the crew (a good preparation and integration to the equipment) is a VITAL "part" of the System (The effective aircraft: System+crew).
Gen. Chuck Yeager in October 1947 successfully landed his bird (X1) after facing a TOTAL electrical failure just after separating from "mother ship".
The fuel valve" (a redundant safety feature) was an important factor to save him and the bird. And the toll (of the failure) was put in him. Who accomplished (partially) the mission. Reducing it to an incident.
PS
One magnificent example was Capt. Sully achievement. (I remember when i crossed Hudson river in a rented motor home). He even flew "offset" the bridge aligning the bus when in the short final. The comment of his wife after learning the fact shows how Sully was the perfect "element" of a well designed System, his bird an the crew.