Tomaski has written a very good thought-provoking post , and it is worth considering the whole philosophy behind checklists, the QRH and SOPs, so, please forgive me for writing at length. In a previous life, I thought long and hard on 'the what' and 'the whys' of SOPs. What was their basis? What was their real purpose? Were they immutable? Why did we need them? Should they always be followed rigidly? Were there ever good reasons to deviate from them?
First, it is necessary, to look at the derivation and purpose of each one – some are required by law, some by the way a piece of equipment works, some are part of the aircraft manufacturer’s operating philosophy, some are part of the airline’s operating philosophy, and some are custom and practice or merely folklore.
A good example of a procedure required by law is the approach ban when the RVR is below limits. In the past it used to be that pilots were allowed to descend to the decision altitude and have a look, but after several accidents CAAs imposed an approach ban. But even this can vary in different countries.
Some items of equipment require rigid operating procedures. For example, when early INS sets were fitted to aircraft, it was necessary to go through a precise alignment process during which the aircraft could not be moved for some ten to fifteen minutes. Also, to guard against false data being entered, each crew member was required independently to check the entered positions and resulting tracks and distances.
During the design and testing of a new aircraft type, the manufacturer will determine a detailed set of normal, abnormal and emergency procedures for such things as fire warnings in engines and/or cargo holds; failure modes in hydraulic and electrical systems; flap and undercarriage malfunctions; runaway stabilsers and normal checklists for pre-start, engine start, taxiing, take-off, after take-off, before descent, landing, after landing and shut-down, etc. This is done in good faith, but cannot, with the best will in the world, cover every eventuality
Most airlines will adopt these without change, but some will modify them depending on their individual operating experiences and mixtures of aircraft types in their fleet. So long as the vital parts of the manufacturer’s checklists and procedures are respected, certain things can be changed. For example which crew member handles the thrust levers and when, which pilot flies the approach and landing and when, who reads and actions the checklists – the pilots or the flight engineer. These changes will be subject to much internal discussion within the airline and also with the CAA and manufacturer.
But some procedures are derived merely from the long established custom and practice of the airline concerned and sometimes for no good reason at all.
The most important thing is that, once established, all crew members must follow these procedures. They are the ‘glue’ that holds the operation together. They are the collective wisdom of all the actors (regulatory authorities, manufacturers, airline) on how best to operate the aircraft safely in the various environments the crew are likely to face. And, very important indeed, they enable the crew members to monitor each other and advise of any departure from the norm.
Thus it will be seen there can be many differences between individual countries – for example, the USA vv Europe; between manufacturers – Airbus vv Boeing; and between individual airlines. All these differences have their merits and demerits, but, once they have been established, all crew members on the flight deck must abide by them for the reasons stated above.
In addition, management should only make changes to the SOPs, for example following an incident or accident, after very careful consideration. And when they do so, with adequate explanation and/or training so that all parties know why the changes have been made and how to apply them.
However, despite all these considerations, it is impossible for the SOPs to cover every eventuality. There then comes the point when they are not appropriate to the situation and the captain decides to deviate from them. This is an extreme measure and should only be done when there is no other option and when the pilot has sufficient knowledge to understand fully the implications of what he is doing. I can think of several examples.
Suppose on take-off at maximum weight in a four engine aircraft (a 747 with multiple landing gears) at a hot and high airfield, birds are ingested into both engines on the same side. Then, when airborne only a few feet above the ground, and barely able to climb, the co-pilot calls positive rate of climb, but the captain elects to leave the gear down until more speed and altitude has been gained. Non-standard, but his reasoning is that the extra drag of the open doors and wheel wells will probably cause the aircraft to sink back towards the ground.
Suppose on final approach all engines suddenly stop. The captain elects to retract the flaps one notch. Non-standard, but the drag reduction is just sufficient to stretch the glide and make the airfield.
Suppose in mid-Atlantic, the underfloor cargo fire warning lights illuminate, the crew have reason to believe the warning is genuine and divert to the Azores. When they arrive the weather has deteriorated, the cross-wind has risen above limits and the cloud base has descended to below decision altitude. There is nowhere else to go and it is imperative to land. They do so successfully. All three examples were genuine events. It is not difficult to dream up other scenarios where such actions may be necessary.
And one more to ponder: the Qantas Airbus A380 at Singapore when a turbine disc exploded causing extensive damage and multiple unrelated warnings. In what order should the crew action the various procedures, which should be ignored and which have to be actioned?
My conclusion, therefore, is that normally, flight crews should always obey the SOPs, even in an emergency, yet there may still be times when circumstances may dictate otherwise. Then, and only then, is it permissible and maybe essential to deviate, but this must be done in the full knowledge of ALL the implications. SOPs are for the guidance of wise men and not necessarily to be slavishly followed.
They provide the pathway – the steps to be taken – through the minefield of possible errors so that the crew can carry out all the required actions in the correct sequence, without error and within established limits.
Next, they enable the crew to carry out a well-rehearsed sequence of actions, in much the same way as acquired skills can relieve the thinking part of the brain and so give the individual some spare capacity to think ahead, solve problems and make decisions.
Thirdly, SOPs provide predictability so that crew members can monitor each other and detect and correct errors before they develop into something more serious.
End of philosophical discussion!!