[simion314]

>Because jumping to conclusions is not helpful. Let the NTSB do their job and find out what went wrong

We are used from previous cases that aircrafts will get grounded until we are sure the airplane is not at fault. So why in the past this happened before the investigation was complete but in this case the risk is considered t be minimal? I am not saying that it is right or wrong but I want to understand the algorithm that is used to decide what to do in this cases.

[ubernostrum]

We are used from previous cases that aircrafts will get grounded until we are sure the airplane is not at fault.

To be clear: you're suggesting that grounding an entire type of aircraft, either worldwide or even just within US airspace, is a common response to accidents?

I ask because the last general grounding of a type was in 2013 to remedy the 787 battery issues. Prior to that, the last such grounding was the DC-10 in 1979.

[simion314]

Sorry, my experience was with incidents in my country and my memory could also play tricks on my.

Anyway the question still stands, who and how decides if we should ground some airplanes?

[ubernostrum]

Airlines can voluntarily ground their planes. Manufacturers can recommend it. Generally, only a government agency can force it and they only do so in truly extreme circumstances (often requiring multiple serious incidents). More commonly in the US, a directive will be issued to airlines telling them to carry out some remedy (fix/replace a part, change a procedure, etc.) and a window of time in which to complete it. They don't speculatively ground entire air fleets every time there's a potential problem.

For example, in 1991 a Boeing 737-200 crashed in Colorado with the loss of all lives on board. In 1994 there was another crash of a 737, in Pennsylvania, again killing everyone on board. In both accidents the investigation pointed to unexpected movement of the rudder.

Several other cases were identified where pilots claimed the rudder was moving unexpectedly, but they were able to land safely.

The follow-up took several years of investigative work, and eventually identified a situation where a servo could jam and deflect the rudder.

Despite two severe crashes and many other suspected non-fatal incidents, that generation of 737s was not grounded; the remedy, once the cause had been determined, was an order from the FAA to replace the servos, with a timeline by which the replacement had to be completed.

[WalterBright]

The Smithsonian channel runs a weekly show "Aviation Disasters" which shows in detail how this is done.