Category: Flying

Safety Performance Indicators

What’s happening? Two words, and what seems like the easiest question in the world. Open your phone, look at the screen and a myriad of different sources of information are screaming for your immediate attention. They are all saying – look at me, look now, this is vital and don’t miss out. Naturally, most of us will tune out a big percentage of this attention-grabbing noise. If we didn’t life would be intolerable. The art of living sanely is identifying what matters from the clutter.

So, what happens in aviation when a Chief Executive or Director turns to a Safety Manager and askes – what’s happening? It’s a test of whether that manager’s finger is on the pulse, and they know what’s happening in the real world as it happens.

This is a place I’ve been. It’s a good place to be if you have done your homework. It’s the way trust is built between the key players who carry the safety responsibility within an organisation.

One of the tools in the aviation safety manager’s toolbox is that of Safety Performance Indicators (SPIs). In fact, it’s part of an international standard[1] as part of a package for conducting safety assurance. Technically, we are talking about data-based parameters used for monitoring and assessing safety performance.

The ideas are simple. It’s to create a dashboard that displays up-to-date results of safety analysis so that they can be viewed and discussed. Like your car’s dashboard, it’s not a random set of numbers, bar-charts, and dials. It should be a carefully designed selection of those parameters that are most useful in answering the question that started this short blog.

That information display design requires great care and forethought. Especially if there’s a likelihood that serious actions will be predicated on the information displayed. Seems common sense. Trouble is that there are plenty of examples of how not to do this running around. Here’s a few of the dangers to look out for:

Telling people what the want to hear. A dashboard that glows green all the time it’s useless. If the indicators become a way of showing off what a great job the safety department is doing the whole effort loses its meaning. If the dashboard is linked to the boss’s bonus, the danger is that pressure will be applied to make the indicators green.

Excessive volatility. It’s hard to take indicators seriously if they are changing at such a rate that no series of actions are likely to have an impact. Confidence can be destroyed by constantly changing the tune. New information should be presented if it arises rapidly, but a Christmas tree of flashing lights often causes the viewer to disbelieve.

Hardy perennials. There are indicators, like say; the number of reported occurrences, which are broad brush and frequently used. They are useful, if interpreted correctly. Unfortunately, there’s a risk of overreliance upon such general abstractions. They can mask more interesting phenomena. Each operational organisation has a uniqueness that should be reflected in the data gathered, analysed, and displayed.

For each SPI there should be an alert level. It can be a switch from a traffic light indication of green to amber. Then for the more critical parameters there should be a level that is deemed to be unacceptable. Now, that might be a red indicator that triggers a specific set of significant actions. The unscheduled removal or shutdown of a system or equipment may be tolerable up to a certain point. Beyond that threshold there’s serious safety concerns to be urgently addressed.

The situation to avoid is ending up with many indicators that make seeing the “wood from the trees” more difficult than it would otherwise be. Afterall, this important safety tool is intended to focus minds on the riskiest parts of an operation.

[1] ICAO Annex 19 – Safety Management. Appendix 2. Framework for a Safety Management System (SMS). 3. Safety assurance. 3.1 Safety performance monitoring and measurement.

Is Airworthiness dead?

Now, there’s a provocative proposition. Is Airworthiness dead? How you answer may depend somewhat on what you take to be the definition of airworthiness.

I think the place to start is the internationally agreed definition in the ICAO Annexes[1] and associated manuals[2]. Here “Airworthy” is defined as: The status of an aircraft, engine, propeller or part when it conforms to its approved design and is in a condition for safe operation.

Right away we start with a two-part definition. There’s a need for conformity and safety. Some might say that they are one and the same. That is, that conformity with an approved design equals safety. That statement always makes me uneasy given that, however hard we work, we know approved designs are not perfect, and can’t be perfect.

The connection between airworthiness and safety seems obvious. An aircraft deemed unsafe is unlikely to be considered airworthy. However, the caveat there is that centred around the degree of safety. Say, an aircraft maybe considered airworthy enough to make a ferry flight but not to carry passengers on that flight. Safety, that freedom from danger is a particular level of freedom.

At one end is that which is thought to be absolutely safe, and at the other end is a boundary beyond which an aircraft is unsafe. When evaluating what is designated as “unsafe” a whole set of detailed criteria are called into action[3].

Dictionaries often give a simpler definition of airworthiness as “fit to fly.” This is a common definition that is comforting and explainable. Anyone might ask: is a vehicle fit to make a journey through air or across sea[4] or land[5]? That is “fit” in the sense of providing an acceptable means of travel. Acceptable in terms of risk to the vehicle, and any person or cargo travelling or 3rd parties on route. In fact, “worthiness” itself is a question of suitability.

My provocative proposition isn’t aimed at the fundamental need for safety. The part of Airworthiness meaning in a condition for safe operation is universal and indisputable. The part that needs exploring is the part that equates of safety and conformity.

A great deal of my engineering career has been accepting the importance of configuration management[6]. Always ensuring that the intended configuration of systems, equipment or components is exactly what is need for a given activity or situation. Significant resources can be expended ensuing that the given configuration meets a defined specification.

The assumption has always been that once a marker has been set down and proven, then repeating a process will produce a good (safe) outcome. Reproducibility becomes fundamental. When dealing with physical products this works well. It’s the foundation of approved designs.

But what happens when the function and characteristics of a product change as it is used? For example, an expert system learns from experience. On day one, a given set of inputs may produce predicable outputs. On day one hundred, when subject to the same stimulus those outputs may have changed significantly. No longer do we experience steadfast repeatable.

So, what does conformity mean in such situations? There’s the crux of the matter.

[1] ICAO Annex 8, Airworthiness of Aircraft. ISBN 978-92-9231-518-4

[2] ICAO Doc 9760, Airworthiness Manual. ISBN 978-92-9265-135-0

[3] https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-39

[4] Seaworthiness: the fact that a ship is in a good enough condition to travel safely on the sea.

[5] Roadworthy: (of a vehicle) in good enough condition to be driven without danger.

[6] https://www.apm.org.uk/resources/what-is-project-management/what-is-configuration-management/

Objects falling from the sky

In so far as I know, no person on the ground has been killed by an object falling from a commercial aircraft in flight. I’m happy to be corrected if that situation has changed. Strangely, in contrast there are plenty of reports of people falling from aircraft and being killed as a result[1]. Additionally, there are cases of parts shed by aircraft that subsequently contribute to an aircraft accident[2].

The most frequent reports of falling objects, in and around airports are not parts of an aircraft but that which is in the atmosphere all the time. Namely, ice. When it hits the ground in the form of a hailstorm it can be damaging. In flight, it can be seriously damaging to an aircraft.

What I’m writing about here are the third-party risks. That’s when an innocent individual finds themselves the target of an improbable event, some might call an act of God. Ice falls are rare. However, given the volume of worldwide air traffic there’s enough of them to be alert to the problem. As soon as ice accretes to create lumps bigger than a kilo there’s a real danger.

Can ice falls be prevented? Here again there’s no doubt some are because of poor maintenance or other preventable factors, but others are just nature doing its thing. Regulators are always keen to collect data on the phenomena[3]. It’s something that goes on in the background and where the resources allow there can even be follow-up investigations.

Near misses do make the newspaper headlines. The dramatic nature of the events, however rare, can be like a line from a horror movie[4]. Other cases are more a human-interest story than representing a great risk to those on the ground[5].

It’s worth noting that falling objects can be quite different from what they are first reported to be. That can be said about rare events in general.

I remember being told of one case where a sharp metal object fell into a homeowner’s garden. Not nice at all. The immediate reaction was to conclude it came from an aircraft flying overhead. Speculation then started a new story, and the fear of objects falling from aircraft was intensified.

Subsequently, an investigation found that this metal object had more humble terrestrial origins. In a nearby industrial estate a grinding wheel had shattered at highspeed sending debris flying into the air. Parts of which landed in the garden of the unfortunate near-by resident.

One lesson from this tale is that things may not always be as they first seem. Certainly, with falling objects, it’s as well to do an investigation before blaming an aircraft.  

POST 1: There’s a threat outside the atmosphere too. The space industries are ever busier. That old saying about “what goes up, must come down” is true of rockets and space junk. More a hazard to those on the ground, there is still the extreamly unlikly chance of an in-flight aircraft getting hit Unnecessary risks created by uncontrolled rocket reentries | Nature Astronomy

POST 2: EASA Safety Information Bulletin Operations SIB No.: 2022-07 Issued: 28 July 2022, Subject: Re-Entry into Earth’s Atmosphere of Space Debris of Rocket Long March 5B (CZ-5B). This SIB is issued to raise awareness on the expected re-entry into Earth’s atmosphere of the large space object.

[1] https://nypost.com/2019/07/03/man-nearly-killed-by-frozen-body-that-fell-from-plane-is-too-traumatized-to-go-home/

[2] http://concordesst.com/accident/englishreport/12.html

[3] https://www.caa.co.uk/Our-work/Make-a-report-or-complaint/Ice-falls/

[4] https://metro.co.uk/2017/02/16/10kg-block-of-ice-falls-from-plane-and-smashes-through-mans-garage-roof-6453658/

[5] https://www.portsmouth.co.uk/news/national-ice-block-falls-aircraft-and-smashes-familys-garden-1078494

Social media is changing aviation safety

You may ask, how do I sustain that statement? Well, it’s not so difficult. My perspective that of one who spent years, decades in-fact, digging through accident, incident, and occurrence reports, following them up and trying to make sense of the direction aviation safety was taking.

In the 1990s, the growth of digital technology was seen as a huge boon that would help safety professionals in every way. It was difficult to see a downside. Really comprehensive databases, search capabilities and computational tools made generating safety analysis reports much faster and simpler. Getting better information to key decision-makers surely contributed to an improvement in global aviation safety. It started the ball rolling on a move to a more performance-based form of safety regulation. That ball continues to roll slowly forward but the subject has proved to be not without difficulties.

Digging through paper-based reports, that overfilled in-trays, no longer stresses-out technical specialist quite the same as it did. Answers are more accessible and can reflect the real world of daily aircraft operations. Well, that is the theory, at least. As is often the case with an expansion of a technical capability, this can lead to more questions and higher demands for accuracy, coverage, and veracity. It’s a dynamic situation.

Where data becomes public, media attention is always drawn to passenger aircraft accidents and incidents. The first questions are always about what and where it happened. A descriptive narrative. Not long after those questions comes: how and why it happened. The speed at which questions arise often depends on the severity of the event. Unlike road traffic accidents, fatal aviation accidents always command newsprint column inches, airtime, and internet flurries.

Anyone trying to answer such urgent public questions will look for context. Even in the heat of the hottest moments, perspective matters. This is because, thankfully, fatal aviation accidents remain rare. When rare events occur, there can be a reasonable unfamiliarity with their characteristic and implications. We know that knee-jerk reactions can create havoc and often not address real causes.

In the past, access to the safety data needed to construct a context was not immediately available to all commers. Yes, the media often has its “go-to” people that can provide a quick but reliable analysis, but they were few and far between.

This puts the finger on one of the biggest changes in aviation safety in the 2020s. Now, everyone is an expert. The immediacy and speed at which information flows is entirely new. That can be photography and video content from a live event. Because of the compelling nature of pictures, this fuels speculation and theorising. A lot of this is purely ephemeral but it does catch the eye of news makers, politicians, and decision-makers.

So, has anyone studied the impact of social media on developments in aviation safety? Now, there’s a good topic for a thesis.

Safety in numbers. Part 4

In the last 3 parts, we have covered just 2 basic types about failures that can be encountered in any flight. Now, that’s those that effect single systems, and their subsystems and those that impact a whole aircraft as a common effect.

The single failure cases were considered assuming that failures were independent. That is something fails but the effects are contained within one system.

There’s a whole range of other failures where dependencies exist between different systems as they fail. We did mention the relationship between a fuel system and a propulsion system. Their coexistence is obvious. What we need to do is to go beyond the obvious and look for relationships that can be characterised and studied.

At the top of my list is a condition where a cascade of failures ripple through aviation systems. This is when a trigger event starts a set of interconnected responses. Videos of falling dominoes pepper social media and there’s something satisfying about watching them fall one by one.

Aircraft systems cascade failures can start with a relatively minor event. When one failure has the potential to precipitate another it’s important to understand the nature of the dependency that can be hardwired into systems, procedures, or training.

It’s as well to note that a cascade, or avalanche breakdown may not be straightforward as it is with a line of carefully arranged dominos. The classical linear way of representing causal chains is useful. The limitation is that dominant, or hidden interdependencies can exist with multiple potential paths and different sequences of activation.

The next category of failure is a variation on the common-mode theme. This has more to do with the physical positions of systems and equipment on an aircraft. For example, a localised fire, flood, or explosion can defeat built-in redundancies or hardened components.

Earlier we mentioned particular risks. Now, we need to add to the list; bird strike, rotor burst, tyre burst and battery fires. The physical segregation of sub-systems can help address this problem.

Yes, probabilistic methods can be used to calculate likelihood of these failure conditions occurring.

The next category of failure is more a feature of failure rather than a type of failure. Everything we have talked about, so far, may be evident at the moment of occurrence. There can then be opportunities to take mitigating actions to overcome the impact of failure.

What about those aircraft systems failures that are dormant? That is that they remain passive and undetected until a moment when systems activation is needed or there’s demand for a back-up. One example could be just that, an emergency back-up battery that has discharged. It’s then unavailable when it’s needed the most. Design strategies like, pre-flight checks, built-in-test and continuous monitoring can overcome some of these conditions.

Safety in numbers. Part 2

Previously, we walked on a path through some simple statistics as they relate to aircraft systems. Not wishing to sound like the next episode of a popular drama, the only recap needed is, that by making a few assumptions we showed that: where P is the probability of failure and n is the number of similar concurrently operating systems:

A total failure occurs at probability Pn

A single failure occurs at probability n x P

It’s as well to distinguish between the total system and the sub-systems of which it comprises. For example, we can have one aircraft normally operating with four engines. Here we can call each individual engine a sub-system. The word “simple” can best be applied for highly reliable sub-systems where there’s only a few and n is a low number.

Aviation is going through a period of great change. A big part of that change is electrification. Today, there are numerous Quadcopter designs. The name gives it away. Here we are dealing with 4 electric motors connected to rotors. Some new aircraft designs go much further with as many as 18 electric motors. That’s 18 similar sub-systems all contributing to the safe flight and landing of an aircraft.

Superficially, it would be easy to say that if n equals 18 then the chances of the failure of all propulsion simultaneously is astronomically low. That’s true but only if considering the reliability of the electric motors providing propulsion in isolation. Each electric motor makes a partial contribution to the safe performance of the aircraft.

Just as we have with fuel systems in conventional aircraft, in an electric aircraft, each of these sub-systems are dependent upon a source of power being provided. If the source of that power disappears the aircraft’s motor count becomes irrelevant. This is referred to as the consideration of common-mode failures. The electric motors maybe independent in operation but they are all dependent upon the reliable supply of electrical power.

Before a discussion of common-mode failures, let’s go back to the earlier maths. We can see that the loss of one electric motor, amongst 18 occurs with a probability of 18 x P. Unfortunately, in these cases the possible combinations of multiple failures increases.

Given that this subject is so much easier to discuss when dealing with small numbers, let’s consider the Quadcopter. Here there are 4 electric motors and 4 groups of distinct failure condition: 1 motor failed, 2 motors failed, 3 motors failed, and 4 motors failed. For the sake of argument let’s say they perform the same function and call them motors A, B, C and D.

Except for the case where all 4 motors fail, 3 cases produce an outcome with a reduced aircraft capability. We have the way of calculating the probability of total failure and a single failure so it’s the double failure and triple failure cases that are of interest.

Let’s step through the combination of double failures that can occur. Here they are A and B, B and C, C and D, D and A, A and C, B and D. There are 6 unique combinations that make up double failures.

Let’s step through the combination of triple failures that can occur. Here they are A and B and C, B and C and D, C and D and A. D and A and B. There are 4 unique combinations that make up triple failures. We can tabulate these findings for our Quadcopter motor failures thus:

SingleDoubleTripleTotal
4P6P24P3P4

There’s a nice pattern in this table of probabilities. The number of possible combinations of multiple failures grows as n grows.  

Now, we get more into the subject of combinations and permutations. The word “combination” is more often in common usage. When we use that word, it really doesn’t matter what order that any failures occur. Often combinations are like other combinations and so each may not be entirely unique in its impact on the flight of an aircraft. Hence the doubles and triples above.

With 4 electric motors there are 24 possible combinations. This is calculated thus:

n! = n × (n – 1) × (n – 2) × (n – 3)

This is pronounced “n factorial”. So, for n = 18 this gets big. In fact, it’s 6,402,373,705,728,000. 

However, as we have seen from the Quadcopter discussion it’s the grouping of failure conditions that we are often most interested in. Afterall, for safe flight and landing of an aircraft we need to manage those failure conditions that can be managed. At the same time reducing the probability of occurrence of the failure conditions that can’t be managed.

That’s a lot of work. It may explain the drive to develop autonomous aircraft systems. The case could be made that managing flight is impossible when subject to the vast array of potential combinations and permutation of failure conditions that can exist within a multi rotor systems, where n is large.

[Do you agree?]

Safety in numbers. Part 1

It’s a common misconception that the more you have of something the better it is. Well, I say, misconception but in simple cases it’s not a misconception. For safety’s sake, it’s common to have more than one of something. In a classic everyday aircraft that might be two engines, two flight controls, two electrical generators and two pilots, so on.

It seems the most common-sense of common-sense conclusions. That if one thing fails or doesn’t do what it should we have another one to replace it. It’s not always the case that both things work together, all the time, and when one goes the other does the whole job. That’s because, like two aircraft engines, the normal situation is both working together in parallel. There are other situations where a system can be carrying the full load and another one is sitting there keeping an eye on what’s happening ready to take over, if needed.

This week, as with many weeks, thinkers and politicians have been saying we need more people with a STEM education (Science, Technology, Engineering, and Math). Often this seems common-sense and little questioned. However, it’s not always clear that people mean the same things when talking about STEM. Most particularly it’s not always clear what they consider to be Math.

To misquote the famous author H. G. Wells: Statistical thinking may, one day be as necessary as the ability to read and write. His full quote was a bit more impenetrable, but the overall meaning is captured in my shorten version.

To understand how a combination of things work together, or not, some statistical thinking is certainly needed. Fighting against the reaction that maths associated with probabilities can scare people off. Ways to keep our reasoning simple do help.

The sums for dual aircraft systems are not so difficult. That is provided we know that the something we are talking about is reliable in the first place. If it’s not reliable then the story is a different one. For the sake of argument, and considering practical reality let say that the thing we are talking about only fails once every 1000 hours.

What’s that in human terms? It’s a lot less than a year’s worth of daylight hours. That being roughly half of 24 hours x 7 days x 52 weeks = 4368 hours (putting aside location and leap years). In a year, in good health, our bodies operate continuously for that time. For the engineered systems under discussion that may not be the case. We switch the on, and we switch them off, possibly many times in a year.

That’s why we need to consider the amount of time something is exposed to the possibility of failure. We can now use the word “probability” instead of possibility. Chance and likelihood work too. When numerically expressed, probabilities range from 0 to 1. That is zero being when something will never happen and one being when something will always happen.

So, let’s think about any one hour of operation of an engineered system, and use the reliability number from our simple argument. We can liken that, making an assumption, to a probability number of P = 1/1000 or 1 x 10-3 per hour. That gives us a round number that represents the likelihood of failure in any one hour of operation of one system.

Now, back to the start. We have two systems. Maybe two engines. That is two systems that can work independently of each other. It’s true that there are some cases where they may not work independently of each other but let’s park those cases for the moment.

As soon as we have more than one thing we need to talk of combinations. Here the simple question is how many combinations exist for two working systems?

Let’s give them the names A and B. In our simplified world either A or B can work, or not work when needed to work. That’s failed or not failed, said another way. There are normally four combinations that can exist. Displayed in a table this looks like:

A okB ok
A failsB ok
A okB fails
A failsB fails
Table 1

This is all binary. We are not considering any near failure, or other anomalous behaviour that can happen in the real world. We are not considering any operator intervention that switches on or switches off our system. We are looking at the probability of a failure happening in a period of operation of both systems together.

Now, let’s say that the systems A and B each have a known probability of failure.

Thus, the last line of the table becomes: P4 = PA and PB

That is in any given hour of operation the chances of both A and B failing together are the product of their probabilities. Assuming the failures to be random.

Calculating the last line of the table becomes: P4 = PA x PB

In the first line of the table, we have the case of perfection. Simultaneous operation is not interrupted, even though we know both A and B have a likelihood of failure in any one hour of operation.

Thus, the first line becomes: P1 = (1 – PA) x (1 – PB)

Which nicely approximates to P1 = 1, given that 1/1000 is tiny by comparison.

The cases where either A or B fails are in the middle of the table.

P2 = PA x (1 – PB) together with P3 = (1 – PA) x PB

Thus, using the same logic as above the probability of A or B failing is PA + PB

It gets even better if we consider the two systems to be identical. Namely, that probabilities PA and PB  are equal.

A double failure occurs at probability P2

A single failure occurs at probability 2P

So, two systems operating in parallel there’s a decreased the likelihood of a double failure but an increase in the likelihood of a single failure. This can be taken beyond an arrangement with two systems. For an arrangement with four systems, there’s a massively decreased likelihood of a total failure but four times the increase in the likelihood of a single failure. Hence my remark at the beginning. 

[Please let me know if this is in error or there’s a better way of saying it]

Identity

Britan was never part of the Schengen Agreement[1]. I get that. In the days when I was commuting backwards and forwards between the UK and Cologne, Germany, I always had to show my British passport. So, although we once had freedom of movement in the European Union (EU) that document was essential to prove identity. Afterall, we do not have Identity cards (ID) in the UK. Even inside the Schengen Area[2] it’s necessary to carry personal identification. I remember being told off by a policeman for not having ID, other than a UK driver’s licence, on a high-speed train on the trip between Cologne and Brussels. He was fine about it, but it was a friendly – don’t do it again.

Generally, British people do travel overseas. Many of us travel for holidays and business, and in Europe, Spain is one of the most popular destinations.

The number of British people holding a British passport could be well over 80%. This is way ahead of Americans, for example[3]. This doesn’t take account of British passports that may have expired or been lost or destroyed. However, the remarkably large number of British people with passports does underline our love of travel.

I came back from a week’s sunshine in Grand Canary on Monday evening. It’s the second time I’ve been through the airport on that island. Entering the spacious modern airport, the first part of the process is relatively easy. Check-in and drop bags were shared with a great number of tired travellers. Even the hand baggage security check was straightforward.

It’s not until the gate number came up, and the long walk to the far end of the terminal was needed did it appear that the British experience was different. The departure gates were in a glass box wrapped around the end of the terminal. To get into the glass box it was necessary to go through passport control.

For those, like me there were electronic passport barriers. The ques there were shorter than the manual checks. The electronic passport barriers worked. However, on the other side of the glass wall was another que and a uniformed official checking passport. After that there was a desk where each passport had to be stamped. So, that’s 3 checks and an official exit stamp.

So, what’s the value of this added bureaucracy post-Brexit? I have no idea. What’s more upon boarding the aircraft for the flight home, the gate staff check passports again. So, that’s 4 inspections of passenger identity. 5 if the check-in desk procedure is included. British passports may have thick cardboard covers, and secure bindings but their strength as an international travel document has diminished since Brexit.

[1] a treaty which led to the creation of Europe’s Schengen Area, in which internal border checks have largely been abolished.

[2] https://ec.europa.eu/home-affairs/pages/glossary/schengen-agreement_en

[3] https://www.newsweek.com/record-number-americans-traveling-abroad-1377787

Island chaos

Aviation is an international industry. Britain has been “No longer an Island”[1] for over 120 years. As the Wright Brothers demonstrated practical powered flight, so the importance of sea travel began a decline. Nothing in history has shaped the British more than our island status. Living on an island has moulded attitudes, character, and politics.

The illusion of absolute national autonomy and sovereignty is shattered by the interconnection and interdependencies established by flight. Aviation’s growth encouraged a lowering of impediments between nations and geographic regions. In some respects, this has been a two-edged sword. On the one hand, there’s more cooperative working across the globe than there has ever been. On the other hand, conflict crosses natural barriers with much greater ease.

Affordable rapid air travel and growing freedom of movement have been a great boom in my lifetime – the jet age. At the same time, it’s not new that nationalist politicians continue to fear the erosion of difference between the British and the nations of continental Europe, brought about by commercial aviation. Ironically, it’s now the newer digital industries that pose the greatest threat to the illusion of complete independence.

In this context the failure to tackle the critical understaffing at British airports is deep rooted. Lots of finger pointing and experts blaming each other with a catalogue of reasons misses the damage that’s being done by nationalist “conservative” politicians.

Staffing shortages, poor planning and the volume of people looking to travel have led to huge queues and many flight cancellations across UK airports.

Yes, today’s travellers have learnt to take a great deal for granted. They are no longer impressed with the ability to check their emails and watch a movie at 30,000 feet above the sea. So, when the basics go wrong, and flights are seemingly arbitrarily cancelled, queues are long and delays are frequent, the backlash is real.

A UK Minister’s[2] reluctance to restore some freedom of movement to European aviation workers to alleviate the current chaos is an example of blindness to reality. Looking at the historic context, I guess, we should not be surprised that this dogmatic UK Government is so blinkered. Any acknowledgement that the imposition of Brexit is a big factor in airport chaos is far more than their arrogant pride can take. Sadly, expect more problems.

[1] https://www.goodreads.com/book/show/4254465-no-longer-an-island

[2] https://www.independent.co.uk/news/uk/government-transport-secretary-bbc-gatwick-covid-b2092887.html

Past fatal accidents

What can cause an aircraft to plumet from high altitude in an uncontrollable way?

What can cause an aircraft to plumet from high altitude in an uncontrollable way? A selection of accidents come to my mind.

One tragic accident was Indonesia AirAsia Flight 8501, Airbus A320-216[1] in December 2014. Here a malfunction in the rudder control system was reacted to by the crew in an inappropriate way. This fatal accident was put down to pilot error. That is mishandling after an aircraft system failure leading to a stall and plunge into the sea.

The loss of control and crash of Alaska Airlines Flight 261 McDonnell Douglas MD-83[2] in January 2000 is different from the recent Boeing 737 fatal accident but it warrants inspection[3]. For a start the MD-80 series has a high tail and rear engines. However, Flight 261 had a highly experienced crew, but the failure of a critical control component meant the aircraft became unrecoverable. Also, the MD-80 series of aircraft is of a similar generation to the Boeing 737. For both aircraft types, the control of the horizontal stabilizer is necessary to maintain safe flight. The MD-60 accident involved a catastrophic loss of pitch control.

Looking at the sequence of the fatal accident of SilkAir Flight 185, Boeing 737-300[4], in December 1997 it has some similarities. The lead investigators were unable to determine the cause, but suspicion fell on the aircraft rudder controls. This accident remains controversial. The accident flight recorders either stopped because wires broke or because their power was wilfully disconnected. We will never know which was the case.

Again, an accident with an inconclusive report is that of the uncontrolled descent and crash of United Airlines Flight 585. Boeing 737-200[5], March 1991. Anomalies were identified in the accident airplane’s rudder control system, but the accident was not attributed to these problems.

As can be seen from this small sample of accidents the interaction between aircraft and crew, when a control system failure occurs is a matter of great interest.

[1] https://bea.aero/uploads/tx_elydbrapports/Final_Report_PK-AXC-reduite.pdf

[2] https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0201.pdf

[3] https://www.nytimes.com/2000/02/14/us/safety-board-says-wear-was-found-on-jet-in-1997.html

[4] http://knkt.dephub.go.id/knkt/ntsc_aviation/Revised-MI185%20Final%20Report%20(2001).pdf

[5] https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0101.pdf