A top Lufthansa official has warned that the missing flight data recorder may have been too badly damaged when Germanwings flight 4U 9525 crashed in the French Alps.
Lufthansa Board Chairman Kay Kratky said it might not be sending signals.
So far only the cockpit voice recorder has been found at the crash scene, where 150 people lost their lives.
Bad weather has halted helicopter flights to the site, forcing investigators to get there on foot.
An access road to the remote site is being dug by a bulldozer to provide all-terrain vehicles with access to the area and could be completed by Monday evening.
An improved route will help investigators bring heavier recovery equipment to the scene.
French prosecutor Brice Robin has made recovery of the victims a priority. DNA of 80 of the victims has so far been found.
A support centre for victims’ families has been opened at a hotel in Marseille, from where Germanwings plans to provide counselling and visits to the crash site.
Analysis of the voice recorder has suggested co-pilot Andreas Lubitz, 27, crashed the plane deliberately, after locking the pilot out of the cockpit.
A transcript leaked to German media on Sunday revealed how the pilot Patrick Sondenheimer banged on the door, screaming, “Open the damn door!”
While the voice recorder details the pilots’ conversations as well as other sounds from the cockpit, the data recorder includes the plane’s altitude, speed and direction, including the position of the plane’s rudder and flaps.
Appearing on a talk show on German TV on Sunday night, Kay Kratky suggested that a full picture of the accident might never be known as the plane had flown at a speed of 800km/h (500mph) into a vertical rock face and had been pulverised. Mr Kratky’s company Lufthansa fully owns Germanwings.
“It’s possible that the impact was too great for the flight recorder and it doesn’t send signals. However it would still be very helpful to fill out the picture of what happened,” he told the Guenther Jauch show.
There has been criticism of the French prosecutor for releasing details from the voice recorder before a full investigation is complete.
The European Cockpit Association said the release of voice recorder data was a “serious breach” of globally accepted rules. It said many questions remained unanswered.
Revelations have emerged in recent days surrounding the co-pilot’s physical and mental health.
Investigators found anti-depressants at Andreas Lubitz’s house along with evidence of treatment by various doctors, including a torn-up sick note for the day he flew the plane.
There have also been reports that he had problems with his eyesight – possibly a detached retina.
German media reported on Monday that recent medical records had been handed over to investigators by the University hospital in Duesseldorf, relating to three visits made by the co-pilot in February and March. However, details of the visits have not been made public.
Doubs about his fitness to fly have prompted a leading politician from the ruling CDU party, Dirk Fischer, to call for a relaxation of data protection rules governing sensitive jobs such as pilots.
There has also been widespread speculation about Lubitz’s romantic life.
While one unconfirmed report has suggested his long-term girlfriend was pregnant, an ex-girlfriend has revealed that he vowed last year to do something memorable.
“One day I’m going to do something that will change the whole system, and everyone will know my name and remember,” she quoted him as saying.
An official memorial service for those onboard flight 4U 9525 from Barcelona to Duesseldorf will be held on 17 April in Germany’s most famous church – Cologne Cathedral – in the presence of President Joachim Gauck and Chancellor Angela Merkel.