What is NOTAM and why its failure led to grounding of thousands of US flights

Subject: Science and Technology

Context:

Thousands of flights were grounded in the US early Wednesday after a major glitch in the computer system. The US Federal Aviation Administration (FAA) said that flights were grounded due to the failure of a key pilot notification system called Notice to Air Missions (NOTAM).

What is NOTAM?

A NOTAM is a notice containing information essential to personnel concerned with flight operations but not known far enough in advance to be publicized by other means.
- NOTAMs indicate the real-time and abnormal status of the National Airspace System (NAS) impacting every user.
- NOTAMs concern the establishment, condition, or change of any facility, service, procedure or hazard in the NAS.
- NOTAMs have a unique language using special contractions to make communication more efficient.
Without NOTAMs, aeroplanes are at risk of running into flocks of birds or remaining unaware of slippery conditions on runways, for example.
NOTAMs are listed location-wise with pilots needing to check “25 nautical miles to either side of your full route of flight” for relevant NOTAMs.

Example of NOTAM:

The system relays information about changes in conditions such as weather, volcanic activity, airspace restrictions and other factors, as well as unusual events such as parachute jumps, rocket launches and military exercises.
It also advises pilots of extraordinary situations at airports, including icing, malfunctioning lights and the presence of flocks of birds, reported Simple Flying.