Let’s go over the example in the previous post with a fine tooth comb. This analysis should help us understand just how beneficial PDM can be. It will also highlight how in a world without PDM, the long term impact on safety, efficiency and economy(cost) can be adverse.
When the aircraft is enroute between Mumbai and Delhi, the slight increase in EGT was not noted by the pilot since it was within limits. In technical parlance, though, it is precisely these small and gradual changes that indicate to the engineer/mechanic of a developing trend, if not an impending failure. The machine is telling you something. Something that may not create a concern in the immediate future, but is an indication that a fault is in the early stages of development; or, there seems to be a trend in development that will lead to a possible sudden catastrophic failure. If arrested in the early stages, it can save the machinery from further deterioration, which in turn enhances safety besides reducing costs and major delays down the line.
Between Bhopal and Chennai, the EGT comes within the caution range. The pilot makes a note of it in the defect register. However by now, thanks to PDM, all the engineers in the loop are not only aware of the anomaly, but are also aware that the EGT of this particular engine has been showing an upward tend for sometime. So, in other words it doesn’t really come as a surprise to them when the pilot reports it to the AME on arrival. In fact, he’s also had the time (while the aircraft was still enroute to Chennai) to call the AME in Delhi to get some background about the condition and the two would have had a brief chat on what could be the problem.
This is valuable, valuable in terms of time, valuable in understanding the impact on safety, valuable in measuring the impact on operations and what delays might be incurred or saved. Had the AME been hit with the defect of ‘an EGT in the caution range’ straight from the pilot on arrival, without prior warning, his mind would have been racing between what might be the problem, and whether he would have to ground the aircraft for major checks, to what an operational delay might do to the airline and it’s customers. Not to mention he’d have to provide a detailed report to the management the next day on why he delayed a flight for a possibly minor fault.
Coming to Mumbai, which is the major base for the aircraft in terms of availability of special tools, equipment and specially trained manpower. With prior information about the condition of number 2 engine, while the aircraft is enroute between Chennai and Mumbai, the AME will draw out a plan of action. He will have the time and space to make a balanced decision (taking into account safety, reliability, costs, future sectors to be flown etc), call for the necessary equipment, make arrangements to have his team of trained mechanics available and be prepared for the arrival of a reasonably sick engine that somehow needs to be turned around for the flight next day.
And finally, if the AME in Mumbai realizes while working on the engine that it may not be ready for the flight early next morning, he can warn the operations department of the airline to have another aircraft scheduled for next day, or cancel the flight and warn the passengers well in advance.
The difference between having PDM and not, is the Time in(on) your hands!
