Many airline accidents are commonly thought of as being caused by "pilot error". Generally that means "the pilot did not follow approved procedures". But in practice, the approved procedures themselves can indirectly lead the pilots into making many of these "pilot errors".
Manufacturers like Airbus and Boeing recommend the most basic "Standard Operating Procedure" (SOP) traditionally used by most airlines. Unfortunately, this doesn't take account of a number of well-known human weaknesses. If a very simple and long-established alternative was more widely used, most such accidents would be avoided.
What IS the "basic procedure" that you say is inadequate?
Airliners have at least two crew members in the cockpit - the "pilot" and the "co-pilot". The "pilot" is typically the Captain, who is responsible for every aspect of the flight's safety. Normally, the pilot controls where the plane is going (the "flight path") either by hand, or for much of the time nowadays by manipulating the autopilot controls.
The "co-pilot's" main job is assisting the pilot, doing things like communicating with Air Traffic Control, putting the flaps and wheels where the pilot needs them, and operating complex systems like fuel, hydraulics and pressurisation. Just before landing, the co-pilot may have to tell the pilot what is visible outside the cockpit, as the pilot has to land on the runway by what he/she can see.
The co-pilot's other job is to check on what the pilot is actually doing and what's happening to the plane. He or she advises the pilot if things don't seem right, and in an extreme case should forcibly take control if the Captain doesn't react. This is called "monitoring".
So traditionally an airliner's most basic "Standard Operating Procedure" is simply that for the whole of a flight, the Captain is the "Pilot Flying", and the First Officer or co-pilot is the "Pilot Monitoring" . In most airlines, the Captain is free to reverse these roles under some circumstances, but she/he is always in command and responsible for the flight's safety.
So what's wrong with that?
It has three principal flaws. These become most apparent during the most hazardous part of the flight just before landing, especially when the weather is bad. The main weaknesses are
- when problems occur, the pilot gets overloaded with too many things to do at the same time
- it's not safe enough when landing in most "bad weather" conditions
- it can be very difficult for a co-pilot to stop the pilot making mistakes
What's the different procedure?
It's very simple. Before the plane starts its descent to land, the Pilot and the Co-pilot switch tasks. The Pilot concentrates on the overall safe management of the flight, watching for changes in the weather, resolving problems and communicating with Air Traffic Control. The co-pilot flies the plane down until the pilot is sure of making a safe landing. If anything prevents that, the Co-pilot keeps flying the plane so they can try again, or go to a better airport.
This is called a "Pilot-Monitored" approach procedure, because the pilot who will be doing the landing is the "Pilot Monitoring" for the approach phase of the flight. On this website its referred to as the PicMA ("Pilot-in-charge Monitored Approach") procedure. (With similar terminology the traditional procedure would be a "co-pilot monitored" approach, because it has the co-pilot monitoring the pilot.)
Why is that better?
Because it addresses all three of the main problems of the "traditional" SOP.
1. It promotes better planning, and makes managing problems easier.
When the co-pilot organises the approach and the pilot completes the landing, they both have to co-operate and talk about it. Things which one might have forgotten about are picked up by the other. This is essential, especially as the airplane may be flown using an autopilot .
Modern airliners have good autopilots which use lots of computers, which make flying less tiring and more efficient. But like all computers, these can be very attention-demanding. It's easy to get things wrong, especially things that aren't done very frequently. The autopilot doesn't "fly" the airplane in the sense of deciding where to go. It can only do what the pilot tells it to.
An autopilot can't "fly the airplane" on its own just at the press of a button, any more than a washing machine really "does all the laundry". You have to separate the whites and coloureds, make sure the water and electricity are switched on, put detergent and conditioner in the right slots, and selected a program & spin speed before your laundry gets done, and it has to be taken out and put away before you can wear it again.
Computerised systems like washing machines and autopilots actually perform a huge series of very simple tasks very accurately. But if they are told to do something stupid, they can do something very stupid, very accurately. Putting your best sweater in the washing machine without changing to the proper setting can ruin it. It will wash at exactly the temperature on the dial, even if that wasn't what you intended!
And in real life the autopilot has to be given many hundreds of that type of detailed instruction by the pilot, about the height and speed the aircraft should achieve at specific points in the sky and at particular times, in order to complete the flight. If the Pilot isn't actually having to concentrate on all these detailed flying jobs, he or she is much better able to take care of any difficulties and changes that occur - and those are what usually happen just before an accident. For example, the weather might be much worse than expected, or a fault might develop with the plane.
If he isn't actually "flying" the plane, the Pilot can think about "the big picture", such as finding out whether it might really be really better to land somewhere else, without simultaneously having to make lots of detailed changes to keep going with the original plan. The co-pilot is quite capable of doing these detailed tasks, so it spreads the load better if he or she is doing them from the beginning.
NASA research has shown that "PicMA" procedures result in better planning, problem solving and workload distribution.
2. It helps enormously in bad weather. All airliners can fly in cloud and fog, and cockpits have enough instruments that the pilots don't actually NEED to be able to see anything outside for the vast majority of the flight. This is called "instrument flying". However, they do need to see out at the very end of the flight.
Exactly when this need arises varies with the quality of equipment in the plane and on the ground. In a very few cases it is not until after the aircraft has actually touched down ("autoland") but in the vast majority of flights the pilot has to change from "instrument flying" to "visual flying" for at least the final few moments of the flight.
Visual flight means using what he/she can see through the cockpit window. Usually it means that any technical aids like autopilots are no longer usable either. So in this respect even the latest high-technology airplanes are no different to those of the first aviation pioneers over 100 years ago.
Precisely where this must happen depends on the combined accuracy and reliability of the instruments and the radio signals that feed navigation information to them. Generally, it's defined as the lowest safe altitude that it's safe to rely solely on the particular combination of instruments and navigation systems. Typically when the plane reaches this minimum height - "Decision Height" (DA) - it is still half a mile or more from the runway.
For each minimum height, the authorities (governments) lay down visibility conditions that must exist at the airport before the pilot may legally start an approach. It's important to realise that this doesn't mean the plane WILL be able to land - only that there's a fair chance of it. The actual conditions the pilot will encounter may be better, or may be much worse than the pilots expect from reports provided by air traffic control.
Crucially, even if the visibility from the plane at the minimum height is exactly the same as the minimum reported legal value, the pilot will NOT be able to see the runway. In these conditions, what can be seen may only be two or three lights on the ground.
Most people know that when driving in fog, it's best to slow down. The less you can see, the longer it takes to understand what's happening and where you're going. But of course, the pilots can't fly the plane more slowly because there's fog - it always needs the same speed just to keep flying.
The plane is travelling forward at perhaps 180 mph (290km/h) or more, possibly going sideways at as much as 40 mph (65 km/h), and approaching the earth at 12 feet (3.7 m) per second. It takes a significant time for an experienced and trained pilot to determine whether the plane is travelling in the right HORIZONTAL direction from clues like two or three faint lights. The visibility may actually not actually make it possible anyway, while all the time the plane is still descending.
Even if the horizontal path IS correct, the pilot won't be able to tell if its DESCENT is also right until the plane is much closer to the ground - well below the height that the pilot commits to a "visual" landing. If the descent is NOT quite right, it may then be too late to correct it - and a crash will occur. This may sound crazy but it is what regulations allow.
However, although the instruments on their own don't provide enough information to fly safely this low, they do give some information about that aspect, so it's vital that the pilots know what the instruments are reading right down to the ground.
The traditional crew procedure expects the Co-pilot to start looking out for visual cues above the Decision Height, while the Pilot concentrates on ensuring accurate instrument flying. If the co-pilot sees something outside, he or she tells the pilot, who also looks outside, while the co-pilot is supposed to then immediately change back to watching the instruments. The result of this exchange is often catastrophic, because it frequently results in NEITHER pilot watching the instruments at the most critical stage of the approach.
It's important to remember that it has to be the PILOT who decides whether the actual situation allows descent below the DH - not the co-pilot. In marginal conditions, the co-pilot may call out that he can see something just as the plane reaches the Decision Height. This will cause the Pilot to look away from the instruments to assess whatever the co-pilot has seen. The pilot needs a few seconds to reach a decision - by which time the plane will actually be well BELOW the minimum height anyway.
In many marginal situations, limited visual cues cause an illusion that the aircraft is actually HIGHER than it should be. This illusion make the pilot try to "correct the situation" with an steeper descent angle - which causes the plane to crash into the ground short of the runway.
To counter this, the co-pilot is supposed to immediately go back to watching the instruments. But this often doesn't happen, because he or she is still concentrating on trying to make out exactly what is happening outside. This is simply a characteristic of human nature, and if the conditions are right for visual illusions, often both pilots are subject to the same thing. The accident report will then invariably state that the accident was because the pilots "descended below Decision Height without adequate visual reference", in breach of their required procedures.
Of course, it's also quite possible that the Pilot will look up at the DH to discover that what the co-pilot has seen is NOT actually satisfactory for landing. In that case he or she will have to switch back to instrument flying and carry out a "missed approach" or "go-around". Each adjustment takes a finite time, during which the plane continues to get closer to the ground. It is inevitably lower than its legal minimum height and at risk of hitting any obstructions, and having to switch back to instrument flying increases the risk of the pilot losing control of the aircraft. This is because he or she then has to make a very uncommon and dramatic change in its flight path.
It was largely to get around this that the "Monitored Approach" was developed many decades ago. It avoids the problem by specifying that the co-pilot should fly the airplane only using the instruments. A little while before reaching the DH, the Pilot, and ONLY the pilot, starts looking for visual cues. The co-pilot must NOT look out but should stay watching the instruments.
The co-pilot calls for a decision when the instruments show the airplane reaching the minimum height. If the pilot is satisfied by what she or he can see at DH, the pilot takes control to carry out the landing, while the co-pilot continues to watch the instruments. If not, the pilot calls for a go-around or missed approach, and the co-pilot, who has been flying the plane on instruments, is ready prepared to do so.
40 years ago, the United States National Transportation Board made a special study of this type of accident. This recognised all the problems just described. The NTSB recommended changes to crew procedures that can only be achieved by using the Monitored Approach (PicMA) procedure. However the majority of airlines have not made those changes.
3. It makes it much easier to prevent the pilot flying the aircraft making major mistakes.
Checking that what the pilot flying the plane is doing, and what the plane does as a result, is a very important task for a co-pilot, known as "cross-monitoring". A very frequent factor in accidents is that the Pilot makes a significant error, and the co-pilot either goes along with that mistake or doesn't actually do anything about it. Usually this is simply because the Pilot has much more authority than the co-pilot.
In this situation the co-pilot has to change from HELPING the pilot do what he or she intends, to actively PREVENTING it. In the worst cases a First Officer may need to actually take control of the plane from the Captain to stop a dangerous situation continuing. This is extremely hard to do as a Captain has the force of law behind his actions, even if he or she is actually wrong.
The problem is made worse because the Captain is normally also more experienced and better qualified than the First Officer, so he or she can be expected to be more likely to be right in matters of judgment. This is known as the "co-pilot's dilemma".
In principle it's no different to the situation in many other walks of life, where a junior person sees their boss make a mistake. Should you tell the boss she or he is wrong? How do you do you do it? Sometimes, do you even care? it's not your responsibility!
But for a co-pilot it can be literally a matter of life and death for hundreds of people, with only a few moments to decide and no-one else to turn to for advice.
This "cockpit authority gradient" is a well-known problem and airlines have tried to counter it by training, but this has been only partially successful at best, and has been completely ineffective in other cases.
However, it can be completely eliminated just by having the junior person (the co-pilot) actually take the initial role as the pilot flying the plane for that part of the flight. The senior person not only should have better judgment to detect mistakes, but is not inhibited from expressing it.
This is of course built in to the very name of the "Pilot Monitored" approach procedure, as opposed to the traditional procedure's co-pilot monitoring.
The US NTSB described this in a comprehensive study in 1994. It specifically referred to Monitored Approach procedures as a solution to it in their 2000 report into a catastrophic Boeing 747 crash, where the First Officer did not correct the Captain. However, little notice was taken of their recommendation, and the same situation has re-occurred many times since.
If PicMA works, why don't airlines use it?
"Monitored Approaches" have been used for decades by some airlines. Very few incidents have ever occurred where the procedure was actually being used. It is widely recommended in studies on accident prevention. However, many pilots and airlines simply won't consider doing it, because the idea conflicts with traditional training that a pilot has to capable of doing everything during every flight. They resist the idea that both pilots could routinely have a "flying" role during the same flight.
This resistance is reinforced by plane manufacturers whose manuals have to describe the detailed tasks for the "Pilot Flying" and the "Pilot Monitoring". However, manufacturers regard it as the airline's responsibility to decide who should be the "PF" and "PM" in any specific situation.
But airlines often don't want to write down anything that conflicts with what the manufacturers say. Most airlines are under great economic pressure and don't have the time to research this type of problem, especially when in fact accidents are extremely infrequent anyway.
For their part, governments generally accept whatever the airlines put in their manuals if they don't conflict with either actual laws or manufacturers' recommendations.
Consequently, most airlines today still tell their pilots to use "traditional" crew procedures that don't provide the best available protection against the pilots actually making major mistakes.
Accidents are very rare because traditional procedures do work "adequately" most of the time. But situations where it really matters don't occur very often either. If you are on a flight when a number of critical factors coincide, your chances of being in a "pilot error" accident could be much higher, simply because the pilots weren't given the best available ones to prevent it.