In a reversal of regulations implemented post-9/11, small pocketknives and various sporting equipment will soon be permitted in U.S. airplane cabins, according to the Transportation Security Administration (TSA) chief on Tuesday.

Effective April 25, knives with blades under 2.36 inches (6 centimeters) and less than a 1/2 inch wide, as long as they are not fixed or lockable, will be allowed on U.S. flights. Additionally, two golf clubs, toy bats, and sports sticks like ski poles, hockey sticks, lacrosse sticks, or pool cues can be carried in hand luggage.

TSA head John Pistole explained that these changes align the U.S. with international rules and reflect a shift towards “risk-based security.” Enhanced cockpit doors, improved intelligence, and vigilant passengers have diminished the necessity for strict prohibitions on small knives, allowing screeners to focus on detecting more significant threats like bomb components.

However, a union representing 90,000 flight attendants criticized the decision, labeling it “a poor and short-sighted decision by the TSA.” They argued that maintaining the prohibition on these items is crucial for aviation system security.

Although the 9/11 hijackers were widely reported to have used box cutters, the weapons were not recovered, and investigators believe different types of knives were employed. The TSA has gradually eased restrictions on banned items over the years, occasionally expanding the list in response to security concerns.

Under the TSA’s “risk-based security” initiative, the changes aim to streamline the screening process without compromising safety. TSA spokesperson David Castelveter assured that screeners would use “common sense” in applying the rules, avoiding unnecessary delays. The Air Line Pilots Association International praised the effort to harmonize U.S. rules with international standards and endorsed “risk-based security” as beneficial for the industry, airlines, and travelers.

The prospect of a prolonged grounding of Boeing’s new 787 jet is posing a logistical and financial challenge for several airlines, which have already canceled more than 1,000 flights in the 10 days since the plane was grounded worldwide.

Aviation analysts said on Friday that the carriers faced even more uncertainty after investigators in the United States and Japan reported that they had not made much progress in figuring out why two planes experienced serious problems with their volatile lithium-ion batteries.

Without a clear understanding of what happened, all 50 of the 787s delivered to eight airlines over the last 14 months will remain grounded.

The airline with the most at stake, by far, is All Nippon Airways, which bought the first 787 and operates 17 of the planes. It has canceled 459 flights since Jan. 16, affecting more than 58,000 passengers. The airline has used substitute planes or rebooked many of those travelers.

Most of the cancellations were for flights within Japan. But All Nippon also dropped its service between Narita International Airport in Tokyo and San Jose, Calif., and cut in half the number of flights from Tokyo to Seattle. Its latest block of cancellations on Friday included flights for Tuesday through Thursday.

Japan Airlines also said on Friday that it had extended its cancellations to include its flights between Tokyo and Boston on Feb. 2 and 3.

United Airlines, the only American carrier with 787s so far, has been able to maintain its flight schedule with substitute planes.

Most airline executives continue to support Boeing publicly. United’s chairman, Jeffery A. Smisek, said again this week that he thought the fuel-efficient 787 was “terrific” and added that he believed Boeing would come up with a fix soon.

But Richard L. Aboulafia, an aviation analyst at the Teal Group in Fairfax, Va., said officials at some of the airlines had become more nervous in private.

The board’s chairwoman, Deborah A. P. Hersman, said repeatedly at the news conference that a fire should never break out on a plane, as one did on a 787 parked at Logan International Airport in Boston on Jan. 7.

Ms. Hersman’s statements underscored the gravity of the potential hazards for travelers. But Mr. Aboulafia said some aviation officials also interpreted her stark comments as a sign that Boeing faced significant political and public relations hurdles in proving that it could make the planes safe.

“There is an increasing focus in the industry on the risks of politicization,” Mr. Aboulafia said.

He said aviation safety and technology experts believed “there’s still a decent chance of a fix that takes a couple of weeks” if the cause can be clearly identified. If not, he said, “it could become something of a lengthy slog requiring some kind of system redesign and more certification work that could take six months or longer.”

Still, the airlines have few attractive alternatives in the long run and little choice but to wait for Boeing to fix the planes. Thanks to its carbon composite structure and new electrical features, the 787 promises significant savings for airlines that are desperate for ways to cut their fuel bills.

Airbus, Boeing’s big European competitor, is working on a rival to the 787, the A350-XWB. But that plane is not scheduled for delivery until mid-2014, and the program has already had some delays.

As a result, Boeing has not faced any major defection from the airlines, which have around 800 787s on order. United has six of the planes now and two more scheduled for delivery later this year.

“Safety is obviously very important,” Mr. Smisek told analysts on Thursday. “History teaches us that all new aircraft have issues, and the 787 is no different. We continue to have confidence in the aircraft and in Boeing’s ability to fix the issues, just as they have done on every other new aircraft model they have produced.”

But there have been some dissonant voices. Officials with Poland’s national carrier, LOT, have said they will seek monetary compensation from Boeing. Hours before the 787s were grounded worldwide, LOT flew its first commercial flight from Warsaw to Chicago. The plane was not allowed to return, however, after the Federal Aviation Administration and European aviation authorities grounded the planes.

Other operators of 787s are Air India, Ethiopian Airlines, LAN Airlines of Chile and Qatar Airways.

While problems are common with the introduction of jet models, analysts said Boeing needed to keep travelers from losing confidence in the plane.

The battery problems have already created buzz on online forums. One comment, on the Cranky Flier blog, noted: “Let somebody else play the guinea pig for a while first. When commercial airlines manage to operate 787 flights on a daily basis for a month or two without significant mishap, then I’ll consider it safe.”

United Airlines has placed an order for 150 Boeing 737 jets, amounting to $14.7 billion at list prices.

Announced in Chicago, the corporate hub for both companies, the deal includes 100 of the 737 MAX 9 and 50 of the 737-900ER extended-range jets. The delivery of these jets is scheduled between 2013 and 2022, with additional options for more aircraft included in the deal.

The negotiations for the deal, lasting about a year, were characterized by Jeff Smisek, CEO of United parent United Continental Holdings. He emphasized that the new jets would be more reliable and significantly more efficient, reducing fuel consumption by approximately 15% compared to the aircraft they are replacing.

Boeing’s exclusive role as the supplier for this order marks a triumph for the aircraft manufacturer in its competition with European rival Airbus. United had discussions with both Airbus and Boeing before opting for Boeing as its sole supplier for this order, the first since the 2010 merger of United and Continental.

This order represents Boeing’s largest since the record-breaking $22 billion sale of 230 various 737 models to Lion Air in November 2011. The 737 MAX 9 will replace some A320 Airbus jets in United’s fleet, but Smisek clarified that United will continue to have Airbus aircraft for an extended period, given its current fleet and existing orders.

Although the announcement was made in Chicago, the order will be factored into Boeing’s total sales at the Farnborough air show outside London. Boeing also revealed orders for 98 other 737 jets from Air Lease Corp. and Virgin Australia. Commitments for an additional 145 jets were made by GE Capital Aviation Services, ALAFCO, and Avalon.

Boeing stated that the cumulative value of all orders and commitments since the start of the air show is $35.6 billion. In comparison, Airbus reported winning about $16.9 billion worth of business for 115 aircraft during the show.

Following the announcement, shares of Airbus parent European Aeronautic Defence and Space Co. fell 1.2%, while Boeing’s shares slipped 0.5%. United Continental’s shares experienced a 5% decline.