Previous Post

14 Dec 2009

Boeing Dreamliner 787 validated for test flight – based on what?

Posted by Hans van der Zanden

When lessons learned from history may provide any guideline there is something serious to worry about validation of Boeing’s new all composite aircraft.

December 10th 2009, Boeing reported that “the program has validated the airplane structure for the 787 Dreamliner”, and announced that, subject to weather conditions, Dreamliner one is expected to make its first flight within a week or so. First flight will take place very careful, with sunny conditions and limited wind, and no problems are expected. For the moment the whole first flight exercise is to appease reporters and investors. Once the window is extended conditions get more severe and serious problems will undoubtedly surface, and one can only hope and pray that nobody gets killed. Not since the Comet has a civil aircraft been so badly  prepared for flight testing.

Difficult to depict on what grounds the structure of the aircraft has been validated. As was argued in the previous post, the aircraft is without reliable model. All main structural tests performed so far – wing box, blow test and wing bending test – failed by wide margin from the modeled predictions. Each time the structure required comprehensive strengthening, provisionally applied, and only the wing box sustained ultimate load. The blow test has not even been repeated, nor has properly strengthening been performed leaving the planes with thousands of wrongly place fasteners. Remember that it took only a wrongly chosen O-ring to destroy the Challenger. The repeated wing bending test has been performed to limit load only, that is two third of the load required for specification. Validation cannot be described otherwise than based on wishful modeling.

Another aspect that has to be considered is that the test flight aircraft differ in significant way from the ground structures that have been tested so far, and are dissimilar. Each of these aircraft present a differing structure, that is with multiple specific modifications, redesigns and repairs, when Boeing and its partners slowly learned to deal with composites – the extend of which deviations is not clearly known to Boeing. It would be interesting just to learn about the weight of each basic structure and the numbers and types of fasteners applied in each of the flight test aircraft. This means that these aircraft will behave differently, for the better or the worse, leaving the models ineffective.

Remember that structural problems with the Comet surfaced once the planes were in service, as was also the case with for example the F111. So many were killed, so many tragic accidents could have been easily avoided given ample time for reasoning and development. The question is, why were they killed.

Management and engineers at Boeing – and for that part the FAA – are under immense pressure to deliver what is physically virtually impossible. Stakes have probably never been so high in corporate history. One can doubt the design rationale, that is argumentation and justification leading to the decision to validate the structure – sound reasoning cast in shadow by commercial interests. This went terribly wrong with the Comet, and played also havoc with the accident of the Columbia and when the Space shuttle Columbia was still in orbit. In hindsight, the causes that led to these accidents are similar, too much pressure leading to ignorance. All involved now at Boeing are undoubtedly well aware that with these past accidents nobody was convicted for such behavior, too much at stake. This may be poor comfort for those facing the rising sun, let the lessons learned therefore serve at least to avoid future ignorance.

Boeing is presently at crossroads to decide whether to proceed with their all composite adventure, now the advantage of lightweight has diminished . Be aware that it will take years and much more resources to develop a reliable and safe all composite aircraft – probably another thousand days to come if ever – so much unfinished business and issues that have not been properly approached and researched. Ignorance will inevitably lead to a repeat of the Comet.

Ignorance that led to the accidents with the Comet, Concorde and Columbia is further detailed in separate chapters that can be downloaded at this site.

Subscribe to Comments

2 Responses to “Boeing Dreamliner 787 validated for test flight – based on what?”

  1. AIRWORTHY IS BASED ON A DESIGN THAT MEETS THE APPLICABLE AIRWORTIHNESS STANDARD – IN THIS CASE, THE 787, THE STANDARD IS 14 CFR PART 25.
    ONCE THE DESIGN IS APPROVED BY AN FAA DESIGNATED ENGINEERING REPRESENTATIVE (DER) AND THE DRAWINGS AND UPPOTING REPORTS ARE COMPLETE PARTS CAN BE PRODUCED. EACH PART PRODUCED HAS TO BE INSPECTED BY ANOTHER FAA DESIGNATED PERSON – A DESIGNATED AIRWORTHINESS REPRESENTATIVE (DAR) TO VERIFY THE PART CONFORMS TO THE APPROVED DRAWINGS. THEN, AND ONLY THEN, SHOULD THE PARTS BE ASSEMBLED AND THE FULL SCALE GROUND AND FLIGHT TEST BEGIN.
    CHANGES TO PARTS DURING THE ASSEMBLY AND TEST PROCESS MUST BE DER APPROVED, THE DRAWINGS REVISED AND THE MODIFIED PART MUST BE INSPECTED TO VERIFY CONFORMITY TO THE DRAWING OF THE PART BY A DAR BEFORE IT IS INSTALLED. TIME CONSUMING, YES. THE PROCESS IS DIFFICULT WHEN ALL OF THE PARTS UNDER CONTROL OF THE “ASSEMBLER”. DOING IT ON A GLOBAL BASIS IS MORE DIFFICULT. BASED ON PUBLISHED PROBLEMS I DOUBT THAT THE PROCESS DESCRIBED ABOVE HAS BEEN FOLLOWED TO THE “LETTER OF THE LAW”. fURTHER, I CAN’T UNDERSTAND HOW YOU CAN BYPASS LOAD AND FATIGUE TESTING AND STILL DESCRIBE THE PARTS AS “CONFORMING TO TYPE DESIGN AND IN CONDITION FOR SAFE OPERATION” – THE DEFINITION OF “AIRWORTHY”.
    MY COMMENT IS BASED ON MORE THAN FIFTY YEARS OF EXPERIENCE WITH LARGE AIRCRAFT – INCLUDING 25 YEARS AS A DAR.
    JIM HELMS
    1-650-212-2916

     

    JIM HELMS

  2. TYPO IN SECOND SENTENCE – “UPPORTING” SHOULD BE “SUPPORTING”.

     

    JIM HELMS

Leave a Reply

Message: