Flight No. 191 associated with previous emergencies

JetBlue Flight 191's in-air emergency Tuesday ended without injury.

But at least three other flights with 191 in the number have seen tragic ends, and a fourth was involved in a scary incident, a fact noted in the Twitterverse.

"Do u see a pattern: AA191=crashed, DL191=crashed, Comair5191=crashed, Southwest1919=semi-crashed, #Jetblue 191-could have crashed. #Flt191," tweeted @clubnonrev, a social media feed for a Club

NonRev.com website that bills itself as a resource for airline staff, retirees, family and friends.

AA191 refers to American Airlines Flight 191, which lost an engine shortly after lift-off from Chicago O'Hare International Airport on May 25, 1979. The plane crashed to the ground less than a mile from the runway, killing all 271 people on board and two on the ground, according to Chicago Tribune archives.

Six years later, on Aug. 3, 1985, 135 people aboard Delta Airlines Flight 191 perished when an L-1011 wide-body jet en route from Fort Lauderdale, Fla., to Los Angeles crashed on final approach for a stop at the Dallas Fort Worth International Airport, Dallas Morning News archives show. An air downburst and extremes of shifting winds shoved the aircraft to the ground, causing the Federal Aviation Administration to mandate that all airliners have wind-shear detection systems by 1993.

Comair Flight 5191 crashed on takeoff from Lexington, Ky.'s, Blue Grass Airport on Aug. 27, 2006, killing 49, according to the Lexington Herald-Leader.

Southwest Airlines Flight 1919 from Denver skidded off a runway on landing at Chicago Midway International Airport in April 2011, but no one was hurt in the incident, a USA Today report said.

Airlines generally have wide latitude in assigning flight numbers, said Seth Kaplan, managing partner of Airline Weekly.

"Every airline has a different way of doing it," Kaplan said. "Typically, you start with odd-numbered flights all going in one direction and even-numbered flights going in the other. A flight in one direction might be Flight 1 and the return might be Flight 2."

Flight identifiers with more digits tend to denote flights of larger airlines' regional carriers, Kaplan said.

Many airlines will use low numbers to mark flagship routes, and international carriers have sometimes tailored numbers to embrace numbers deemed lucky and avoid numbers deemed unlucky in other countries and cultures, he said.

"And when there's an incident, certainly an incident involving fatalities, an airline (itself) will usually retire that number," Kaplan said.