By Andy Pasztor, Jon Ostrower and Robert Wall 

With lack of security seriously compromising the on-site probe into Malaysia Airlines Flight 17, hopes of getting clear-cut answers from its "black box" recorders also may end up a major disappointment.

The devices are older versions likely to provide only limited information regarding the sequence of events following the presumed missile strike on the plane, according to air-safety experts.

Both the flight-data and cockpit-voice recorder were manufactured in the mid-1990s, years before regulators mandated that such devices on new jetliners include larger memories, faster recording speeds and backup battery power in case onboard electrical systems suddenly fail. The U.S. Federal Aviation Administration didn't mandate retrofits of backup power.

The result, these experts said, is that investigators are likely to end up with sketchy data about the seconds immediately after the ground-to-air missile hit. The cockpit-voice recorder may not have much beyond the sounds of the impact, they said.

The age of the recorders combined with the extent of damage to the plane, according to outside experts, also means that investigators may not get a clear-cut pattern of cascading equipment failures as the fuselage of the Boeing 777 is assumed to have ruptured, with parts breaking off and the aircraft subsequently plummeting to the ground, killing all 298 people aboard.

Malaysia Airlines and Honeywell International Inc., which made the recorders, said the devices didn't have any backup electrical power. If the initial impact of the missile severed critical electrical and computer connections to the front of the plane, the cockpit-voice recorder would have stopped working within one-quarter of a second, according to industry officials.

"The plane probably lost much of its electrical power almost immediately, " according to Alan Diehl, a former Pentagon and U.S. National Transportation Safety Board investigator. "Unlike most accidents, I don't think the recorders are going to help explain very much" about pilot reactions or the plane's disintegration.

Amid the escalating public focus on what the black boxes may reveal, British investigators analyzing them said over the weekend that "we don't comment on operational matters."

The Dutch Safety Board, which is in charge of the overall probe, previously said it successfully downloaded information from both recorders. But it didn't elaborate on how much of the recovered data originally were recorded before the presumed missile strike. Boeing didn't immediately respond to questions.

Over the weekend, Dutch investigators said they weren't ready to discuss details of the probe. The entire international team of investigators working on Flight 17 has had to promise to refrain from prematurely divulging details. Regulators and industry officials from several countries, however, project that some preliminary findings could be made public around the end of the month.

Ukrainian, U.S. and U.K. authorities have said they believe a sophisticated surface-to-air missile, fired from an area controlled by pro-Russian separatists, brought down the plane. They also said there isn't any credible evidence indicating another cause. With international investigators largely kept from the site, safety experts emphasized the challenge of collecting remnants of the plane for detailed chemical and metallurgical analyses seeking residue from a missile.

Experts said a fuselage break would have sent hurricane-force winds of about 300 miles an hour through the interior, breaking electrical conduits, smashing remnants of the cabin and other parts into some passengers. Debris spotted on the ground appears to be spread over at least 6 miles and across three Ukrainian villages, suggesting an in-flight breakup that may have severed the plane's forward section from its electricity-generating engines.

From sounds likely captured in the cockpit, "the best you may get is the pilots saying what the hell is that,'" said John Cox, a former airline pilot and air-accident investigator for a pilot union who now runs a consulting firm in Washington.

At best, "the sequence of system failures might give investigators a better handle on what part of the plane received the initial impact," Mr. Cox said.

Major portions of the front of the jet, including the electronics bay that distributes power to aircraft systems, landed in a sunflower field around 4 miles from the largest concentration of debris containing the jet's engines and wings.

The flight-data recorder presumably will provide definitive altitude, speed, heading and location information before impact, as well as whether engines or other onboard equipment were operating normally. But unless that device continued to receive full power and uninterrupted data during the jet's breakup--something many experts consider unlikely--downloading its contents probably won't yield all of the answers investigators seek.

"Once the plane starts falling apart, a lot of things get disconnected and you lose" vital information from system sensors as well as what was occurring on the flight deck, said Dick Healing, a former member of the U.S. National Transportation Safety Board.

Ten days after Flight 17 went down, the precise capabilities of its cockpit recorder remained unclear. A Honeywell spokesman said the device, manufactured in December 1996, has a 30-minute memory and keeps recording over older audio recorded in the cockpit. In response to questions, Malaysia Airlines said the device records the last two hours of sounds in the cockpit, which is today's standard.

Jason Ng contributed to this article.

Write to Andy Pasztor at andy.pasztor@wsj.com, Jon Ostrower at jon.ostrower@wsj.com and Robert Wall at robert.wall@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires