RECIFE, Brazil – Search crews recovered the vertical stabilizer from the tail section of an Air France jetliner that went down in the Atlantic, Brazil's air force said Monday - a key item in finding the cause of the crash. Eight more bodies also were found, bringing the total recovered to 24 since Air France Flight 447 disappeared with 228 people on board, according to Air Force Col. Henry Munhoz.

In this photo released by the French Defense Ministry on Monday June 8, 2009, divers aboard a French Navy dinghy, foreground, collect a debris near the French frigate 'Ventose', in the search area of Air France's Flight 447 in the Atlantic ocean. [Agencies]

The discoveries of debris and the bodies are all helping searchers narrow their search for the jet's black boxes, perhaps investigators best hope of learning what happened to the flight.

Brazilian military officials have refused to detail the large pieces of the plane they have found. But a video on the Brazilian air force website entitled "Vertical Stabilizer Found" shows video of the piece — which keeps the plane's nose from swinging from side to side — being located and tethered to a ship. The part had Air France's blue-and-red stripes, retained its triangular shape and bore no evident burn marks.

Investigators are looking at the possibility that external speed monitors — called Pitot tubes — iced over and gave dangerously false readings to cockpit computers in a thunderstorm.

Peter Goelz, a former managing director of the National Transportation Safety Board, said the faulty airspeed readings and the fact the vertical stabilizer was sheared from the jet could be related — though he cautioned it would need to be determined if the stabilizer was torn off in flight or upon impact in the ocean.

The Airbus A330-200 has a "rudder limiter" which constricts how much the rudder can move at high speeds — if it were to move to far while traveling fast, it could shear off, and take the vertical stabilizer with it as they are attached.

"If you had a wrong speed being fed to the computer by the Pitot tube, it might allow the rudder to over travel," Goelz said. "The limiter limits the travel of the rudder at high speeds and prevents it from being torn off."

Asked if the rudder or stabilizer being sheared off could have brought the jet down, Goelz said: "Absolutely. You need a rudder. And you need the (rudder) limiter on there to make sure the rudder doesn't get torn off or cause havoc with the plane's aerodynamics."

Some high-tech help is on the way for investigators — two US Navy devices capable of picking up the flight recorders' emergency beacons far below on the ocean floor. What caused the Airbus A330-200 to plunge into the middle of the ocean on May 31 with 228 people on board might not be known until those black boxes are found.

An internal memo sent to Air France pilots Monday and obtained by The Associated Press urges them to refuse to fly unless at least two of the three Pitot sensors on each planes have been replaced.

The leader of another pilots' union, however, said Monday that Pitot troubles probably didn't cause the Flight 447 disaster.

Searchers must move quickly to find answers in the cockpit voice and data recorders, because acoustic pingers on the boxes begin to fade 30 days after crashes.

While large pieces of plane debris — along with 24 bodies — has helped narrow the search, it remains a daunting task in waters up to 1.5 miles (2.5 kilometers) deep and an ocean floor marked by rugged mountains.

"Finding the debris helps because you can eliminate a large part of the ocean," said US Air Force Col. Willie Berges, chief of the US military liaison office in Brazil and commander of the American military forces supporting the search operation.

But ocean currents over the eight days since the disaster have pushed floating wreckage far and wide, complicating the search, Berges said. "In the sense that as the debris drifts away, you're not sure exactly where the black boxes or other parts of the aircraft are on the bottom of the ocean."

The US Navy has helped locate black boxes in difficult situations before: pings from an Adam Air jet that crashed Jan. 1, 2007, off Indonesia's coast were picked up 25 days later by a navy team.

The two towed pinger locators the US is sending are expected to arrive in Brazil late Monday and will be dropped into the ocean near the debris field by Thursday, Berges said. The search is focusing on several hundred square miles (square kilometers) roughly 400 miles (640 kilometers) northeast of the Fernando de Noronha islands off Brazil's northern coast.

The listening devices themselves are five-feet long and weigh 70 pounds. One will be towed by a Brazilian ship, the other by a French vessel, slowly trawling in a grid pattern across the search area. The devices can detect emergency beacons to a depth of 20,000 feet (6,100 meters).

Cables attached to the devices lead to on-board computers, enabling a 10-person team that accompanies each device to listen for pings and to visually see them on a screen, like a radar spotting objects in air.

The French nuclear attack submarine Emeraude, arriving later this week, also will try to find the acoustic pings, military spokesman Christophe Prazuck said.

If the pings are located, French deep-water unmanned subs aboard the oceanographic survey ship Pourquoi Pas will attempt to retrieve the boxes from the ocean floor.

This area of the Atlantic Ocean is littered with floating garbage, vexing the initial search effort. Days after the plane went down, the weather let up and bodies began to surface, giving searchers more to go on.

Twenty-four bodies were recovered since Saturday about 45 miles (70 kilometers) from where the jet was last heard from.

Searchers also spotted two airplane seats and debris with Air France's logo, and recovered dozens of structural components from the plane. They had already recovered jet wing fragments, and said hundreds of personal items believed to from passengers were plucked from the water.

France is leading the investigation into the cause, while Brazil focuses on the recovery of bodies and wreckage.

Brazil says the search area lies southeast of the jet's last transmission — automatic messages signaling catastrophic electrical failure and loss of cabin pressure. The messages mean Flight 447 likely broke apart in turbulent weather while flying from Rio de Janeiro to Paris. The location of the wreckage could mean the pilot was trying to turn around in mid-flight.

The L-shaped metal Pitot tubes jut from the wing or fuselage of a plane, and are heated to prevent icing. The pressure of air entering the tubes lets sensors measure the speed and angle of flight. An iced-over, blocked or malfunctioning Pitot tube could cause an airspeed sensor to fail, and lead the computer controlling the plane to accelerate or decelerate in a potentially dangerous fashion.

Air France said it began replacing the Pitot tubes on the Airbus A330 model on April 27 after an improved version became available, and will finish the work in the "coming weeks." The monitors had not yet been replaced on the plane that crashed.

An official with the Alter union, speaking on condition of anonymity because the memo was not publicly released, said there is a "strong presumption" among their pilot members that a Pitot problem precipitated the crash. The memo says the airline should have grounded all A330 and A340 jets pending the replacement, and warns of a "real risk of loss of control" due to Pitot problems.

France's investigating agency said the messages suggest the plane received inconsistent airspeed readings from different instruments as it struggled in a violent thunderstorm.

But the secretary general of another French pilots' union, SNPL, said Monday the tubes were not likely the cause of the crash. Pitots are "a possible contributing factor," Julien Gourguechon said, but even without them, "we can make the plane fly."