An aviation expert has questioned whether the doomed Germanwings passenger plane may had its electronics 'hacked' before it crashed killing all 150 on board. The theory has surfaced in a letter to the respected Financial Times newspaper from aviation boss Matt Andersson, president of Chicago-based Indigo Aerospace. The French Alps tragedy which occurred on the flight between Barcelona to Dusseldorf has been widely blamed on co-pilot Andreas Lubitz, 28. He is believed to have barricaded himself in the cockpit of the GermanWings A320 Airbus before flying the packed plane into the mountainside as the captain fought desperately to get inside. Scroll down for video . Disaster: An aviation expert says an external factor like 'electronic hacking' could have been to blame for the Germanwings plane crash that claimed 150 lives . Tragedy: The crash in the Alps has been blamed on the co-pilot Andreas Lubitz who investigators say locked himself in the cockpit and deliberately crashed the jet . Investigation: But Matt Andersson - president of Chicago-based Indigo Aerospace - says any number of causes could have caused the crash . Doomed: Recordings from the cockpit suggested that co-pilot Andreas Lubitz (left) locked himself in the cockpit while the Captain Patrick Sondenheimer desperately tried to break in . Investigators point to a history of mental illness and doctors notes which were hidden from his employer. Mr Andersson says the French accident investigators are clear that the stricken plane 'accelerated in its descent'. But he writes in the FT: 'That may be, but it could be from any number of causes, including external electronic hacking into the aircraft's control and navigation systems through malware or electromagnetic interception.' 'This is one reason military and head-of-state aircraft are generally installed with specific shielding and additional active protective measures,' and he stresses: 'Civilian aircraft are not.' Mr Andersson says the public should reserve final judgment until the investigators have completed their enquiries and come to a firm conclusion. He added: 'The public should patiently wait for a through, multi-party professional air safety investigation, while maintaining an independence of judgment over preliminary official hypotheses.' Setting out his doubts about jumping to conclusions based on preliminary findings, Mr Andersson said: 'Both the cockpit voice recorder (CVR) and the flight data recorder (FDR) of the Germanwings flight 9525 have yet to be subject to international standards. 'Until they are, many broad assertions currently presented to the public may turn out to be erroneous, misleading or in some cases lead to improper or counterproductive regulatory and other reactions –including misplaced liability, financial and insurance claims.' Damaged: Despite revelations from the plane's flight data recorders (pictured), Mr Andersson says the public should reserve final judgment until the investigators have completed their enquiries . Aftermath: He claims passenger planes do not have the same level of protection as military jets and someone could have hacked into its 'control and navigation systems through malware or electromagnetic interception' Since the crash, European air safety chiefs have recommended that two people must remain at all times on the flight deck, requiring a member of cabin crew to step in if one of the two pilots leaves the cockpit. Mr Andersson writes in the FT that the 'slow drip' of piecemeal judgments from preliminary assessments of data can be counterproductive. He said the European Cockpit Association representing nearly 40,000 professional pilots 'has rightly criticised the premature release' of the aircraft's cockpit voice recorder. Investigators say this highlights the co-pilot breathing while locked in the cockpit while the pilot beats on the door outside. Protection: Since the crash which is believed to be caused by 28-year-old co-pilot Andreas Lubitz (pictured), European air safety chiefs have recommended that two people must remain at all times on the flight deck . Police carried out forensic searches on Lubitz's and his parents house after it emerged that he 'deliberately' crashed the Airbus A320 jet into the Alps . He believes premature release 'could arguably prejudice a formal technical assessment' and Mr Andersson is not the only aviation expert to speculate on the plane being 'hacked'. Former commercial pilot Jay Rollins told US television channel MSNBC last month: 'This aircraft is highly computerised. 'There's one possibility that no-one has brought up. I wonder – could this be a hacking incident?' He drew parallels with the loss of a US drone over Iran, which some blamed on electronic hacking: 'Suddenly the aircraft responding to outside forces. 'If something like that were going on it would be very disturbing for the pilot.'
'Electronic hacking' could have caused the air disaster, aviation boss says .
Germanwings tragedy has been widely blamed on co-pilot Andreas Lubitz .
But Matt Andersson says investigators have yet to come to a final conclusion .
Says passenger planes do not have same level of protection as military jets .