'Torque is cheap' – a plaintiff must still prove that the defendant's negligence caused the loss – Robinson Helicopter Company Incorporated v McDermott [2016] HCA 22

The plaintiff was a passenger in a helicopter which was manufactured by Robinson Helicopter Company Incorporated (the defendant). During the course of a flight, the helicopter crashed and as a result the pilot was killed and the plaintiff suffered serious injuries.

The cause of the crash was a failure of the helicopter's forward flex plate. The flex plate was part of the helicopter's drive system, which transferred torque (a measure of the twisting or rotational force acting upon an object) from the helicopter's engine to the main rotor gearbox. At each point of the star-shaped flex plate there was a bolt which secured the flex plate in the drive system.

The flex plate was required to withstand considerable stress and was capable of doing so as long as each of its four bolts were tightened to the requisite degree. The manual issued by the defendant required that torque seal (paint) be applied to all critical fasteners in a stripe across both nuts and exposed bolt threads. When applied correctly, the part of the stripe which was painted across the nuts and bolt aligned with the part of the stripe which was painted on the horizontal clamped surface that the bolt was fastened to.

There was no dispute that the flex plate failed and the crash occurred because, contrary to instructions given in the manual, one of the four bolts securing the flex plate was incorrectly assembled and was not tightened to the requisite degree. The defendant did not cause the defect and it was not known who did. The focus of the proceedings was not so much on when and how the defect arose, but instead as to whether the manual provided sufficient instructions to facilitate detection of the defect at subsequent inspections.

First instance decision²

In the first instance, it was held that the explanation given in the manual of the function of the torque stripes, coupled with the instruction given in the manual to "verify security", was sufficient to convey to a person carrying out a regular inspection that it was necessary to look for a torque stripe on each flex plate bolt and if it were "missing, damaged, or incomplete", to take steps to determine whether the bolt was correctly torqued, to re-torque the bolt and then to apply a fresh torque stripe.

It followed that it was not established that the manual was inadequate to address the risk of flex plate failure resulting from an inadequately torqued bolt. Accordingly, the trial judge found for the defendant.

Queensland Court of Appeal (Court of Appeal) decision³

The majority of the Court of Appeal held, inter alia, that the trial judge had erred in finding on the evidence that it was probable that a torque stripe was not applied when the bolt was incorrectly assembled. Further, the Court of Appeal held that the trial judge was not correct in limiting the range of possibilities to a missing or misaligned torque stripe. It was possible that if the torque stripe was applied to a dirty or greasy surface, it may have been able to rotate with the bolt.

The majority held that the manual was defective in failing to make it clear to persons inspecting the bolt that the visual inspection of torque stripes may not be sufficient to indicate whether critical fasteners were correctly assembled. Further, if the manual had contained an additional simple instruction to check the torque of critical fasteners with a torque wrench or a simple spanner, the persons who conducted the subsequent inspections would have followed that instruction and inevitably detected the incorrectly assembled bolt.

The Court of Appeal allowed the appeal, finding in favour of the plaintiff.

High Court decision

In a joint judgment, all five justices of the High Court noted that, although the Court of Appeal was conducting an appeal by way of re-hearing, it should not interfere with a trial judge's findings of fact unless they are demonstrated to be wrong by "incontrovertible facts or uncontested testimony", they are "glaringly improbable" or "contrary to compelling inferences". In this case they were not.

It was open to the trial judge to find as he did, either that there was no torque stripe applied to the bolt when it was incorrectly assembled, or if there were a torque stripe completely applied to the bolt at that time, that it would have cracked shortly afterwards and thus would have been misaligned at the time of each of the two '100 hourly' inspections immediately preceding the crash.

Accordingly, the High Court upheld the appeal, finding in favour of the defendant on the basis that it was open to the trial judge to find that there was no breach of duty of care by the defendant. As such, it was not strictly necessary for the High Court to consider the issue of causation. However, it did so in deference to the substantial arguments advanced on that issue.

The High Court noted that the majority of the Court of Appeal had concluded that, if the application of a torque stripe to a dirty or greasy surface were a realistic possibility, there would have been four possibilities, including that a torque stripe was:

1. Not applied when the bolt was incorrectly assembled;
   
   
2. Correctly applied and misaligned so as to provide an inadequate indication of bolt rotation;
   
   
3. Incorrectly applied, so as not to adhere to both the bolt as well as the fixed components, so that the torque stripe could move with the rotating bolt and not crack;
   
   
4. Correctly applied but due to aging, fading or chipping, had to some degree deteriorated.

If possibility three had eventuated (that is, the torque stripe had not adhered to the surface and rotated with the bolt) thereby creating a deceptive appearance of bolt security, it might have been concluded that the defendant owed a duty of care to take reasonable care to avoid that risk eventuating. It might also have been considered that the defendant breached that duty of care by failing to include a direction in the manual that flex plate bolts be checked with a torque wrench at each '100 hourly' inspection.

However, since the manual was adequate to cover possibilities one, two and four, and it was not established that possibility three was any more likely to have occurred than any of the other possibilities, it could not be concluded that the breach of duty in failing to provide for possibility three was causative of the crash.

The High Court has reaffirmed the principle that a trial judge is uniquely in a position to assess the witnesses who are called to give oral evidence, look at physical exhibits and attend views in the course of a lengthy trial. These are advantages which are not available to an appellate court, even when that court is conducting an appeal by way of re-hearing, as opposed to an appeal limited to points of law. If it is open on the evidence for a trial judge to make findings, an appellate court should not disturb those findings.

Although obiter dicta and not essential to its final decision, five justices of the High Court have reaffirmed that a plaintiff must do more than prove that a defendant's negligence has caused that plaintiff to lose the mere chance of a better outcome.

Case managers should be aware that although it may not always be a simple task, particularly where there is complex factual and expert evidence regarding multiple potential causes of an accident, the plaintiff must show not only that the insured was negligent but also that, on the balance of probabilities, the most likely possibility caused the plaintiff's damage. This will often mean working closely with liability experts to identify all possible causes of the accident and their respective likelihoods.

Close consideration should also be given to what the situation would have been if the insured's negligent act or omission had not occurred, that is, whether applying the usual principles of causation, the outcome would have been any different even if the insured had not been negligent.