Research – Page 2 – John Vincent

Sustainable Aviation: Innovations and Challenges

Gas guzzling continues to be one of aviation’s problems. Combustion remains that the heart of most aircraft power plants. Taking large amounts of fossil fuel. Squeezing energy out of every drop of gasoline. Gobbling up more day after day. Pushing out emissions.

As I look out across the garden, I see gliding effortlessly as the warm air rises, a Red Kite[1] gracefully circling. Wings outstretched they hardly move them as they climb. They’re a distinctive small bird of prey, easily spotted because of their forked tail. Now, that’s what I call efficient flying. Using all that nature provides and wasting little energy.

Human attempts at flying are a million miles behind these magnificent birds. There’s still so much to learn about aerial navigation. It’s a matter of control. The sensing of ambient conditions and the precision movements needed to ascend and dive at will.

The search is on for effective change. There’s no pretence that the way commercial aviation operates is unsustainable. It’s true that the gas guzzlers of the air guzzle less gas now than they ever have but the physical facts remain.

None of this is new. I’m about to send a book called “Towards Sustainable Aviation” to a charity shop. It’s not that there’s anything wrong with it. The book is full of pertinent analysis and observations. Trouble is that it’s dated 2003.

I’m led to ask – what’s changed in over 20-years? In answering my own question – quite a lot but not enough. Discourse has moved on from academic quarters to the political sphere. Aircraft have become more fuel efficient. Driven by economic imperatives as much as any concern for the climate. Research initiatives are generously funded to come up with answers. Solutions like hydrogen, electric propulsion, and SAF (sustainable aviation fuel) are slowly moving from theory to practice. A few prototypes are flying. Limited supplies of SAF are flowing.

Unmistakable that’s where the problem lies. For all the hype, policy and government funding the pathway to genuinely sustainable aviation disappears way off into the horizon. There are setbacks too. Gas guzzling is back in fashion. Certainly, in Trump’s America.

We could make a much more of the technology that’s currently available. Yes, there are costs involved. Change is not a free ride. That said, sticking with the status-quo isn’t free either. Legacy costs mount up. One reason why older jets disappeared from fleets so quickly.

The next generation of commercial aircraft must make major steps forward. Since the life of a typical aircraft type can easily extend to 30-years, then change must happen in design now.

Typically, commercial aviation moves with graduated change. There’s an inherent conservatism in the system, as might be expected when safety and security are paramount. Facing this global challenge, there’s a need for a degree more radicalism.

Since high impact disruption is also in fashion, it’s time for airlines and manufacturers to adopt a pioneering spirt. It’s been done before. In the 1960s, that pioneering spirt gave us the Boeing 747, the Jumbo jet. That opened flying to a whole generation.

[1] https://www.rspb.org.uk/birds-and-wildlife/red-kite

Revolution: Hype vs Reality

Talk is of a revolution[1]. That sounds sensational. It sounds like marketing talk aimed at creating an insatiable desire for something new. So, that kind of talk immediately switches on the cynical side of my brain. Is this hype or is it real?

We’ve had plenty of both in my lifetime. Colourful boys adventure books with novelties like nuclear powered aircraft and moonbase vacations. It’s not that “flying a kite” is entirely bad. Those imaginings of the future had pictures of prototype flying cars. Now, we maybe on the verge of that prediction becoming real.

AI is not new. It’s been a research subject for decades. What we have most recently is the coming together of concepts and the practical machines on which to run those concepts. Amazing has been the speed of progress. That’s a modest word considering the sudden adoption of new tools that go way beyond simple INTERNET search engines.

Bill Hunter’s line: “You can’t stop progress”. At least that’s the line I remember of the 1994 film Muriel’s Wedding[2]. It was said on a rocky path to “progress” induced disaster.

My curiosity centres around avoiding the hype and finding out what’s real. That’s in the vain hope that I might not be left behind in this rapid surge of “progress”. So, to keep up with the latest technical developments I clicked on a TED App. The boss of TED, Chris Anderson has recently interviewed Sam Altman, the CEO of OpenAI[3]. He’s the guy behind ChatGPT. AI has elevated new people into the spotlight. It’s given established technology companies a headache. Their desire to be in the pack, or leading the pack is mighty strong.

My takeaways form this interview are that AI will outpace human intelligence, in time. No one knows how much time, but the path is set. The direction of travel isn’t in the control of traditional institutions or government departments. Society must get its head around a time when we live with machines that out pace us.

Second, it would be nice to have an enlightened global regulator to ensure that the massive amount of development going on produces outcomes that are for the public good. Chances of that happening are about zero, although not zero. There’s even a possibility that the industry at work on this technology realises the need for a set of enforceable rules.

Questions of safety are paramount. Even though society debated the impact that the INTERNET would have on us, steps to provide protections and boundaries only came about after the event. Lost in a storage box, I once had a book called “The Sleeping Sentinels”. Basically, the thought was that political parties and the legal profession are always more than ten steps behind the technologists. We are highly reactive.

One interesting aspect of the interview was the pauses. What was evident is that it’s hard to find the right language to describe what’s happening. Walking a tight rope between sounding like Chicken Little[4] and a wise respected elderly professor. Revolution is the right word.

POST: It’s not just IT Why AI Demands a New Breed of Leaders

[1] https://youtu.be/Xv8FBjo1Y8I

[2] https://www.youtube.com/watch?v=PLDcevp5w5o

[3] https://www.ted.com/talks/sam_altman_openai_s_sam_altman_talks_chatgpt_ai_agents_and_superintelligence_live_at_ted2025

[4] https://www.rottentomatoes.com/m/chicken_little

Transform of Future Careers

My education was an industrial one. I guess I was fortunate. No “A” levels for me.

Part of my apprentice programme was to move around the different departments of a major electronics company. That included a range from demanding technical areas, testing new designs, to the everyday pressure of a print room run by an ex-Army man who ran it as if he’d never left the Army. Yes, print rooms were once a staple part of an engineering company. Huge dyeline machines that constantly ponged of ammonia twinned with the noisiest dot-matrix printers ever made. I even got to learn some COBAL[1] with the business unit that put together our payslips. Amazingly enough I was introduced to mathematical concepts, like Fast Fourier Transforms (FFT), at a time when the digital logic needed to implement such algorithms consisted of large cabinet loads of discrete electronics. Now, my simple mobile phone can crunch numbers in this way.

Several weeks here, and several weeks there. One excursion meant spending hot summer days in the Mendip Hills at a quarry testing equipment in deep water. Another meant time working in a former brick-built railway shed that served as a small machine shop.

Of all the different experiences that I had in those formative years (16-18 years) the one that I’ll never forget was a secondment to a London based factory. The company’s training officer recognised that this small village country boy needed to go to the big city. Uppark Drive, Ilford no longer exists as a manufacturing plant. That’s no surprise. In the late 1970s that factory handled the company’s long-lived products. Technology that has gone forever.

Anyway, this is not so much about me. What I’m led to speculate about is what sort of modern-day engineering apprenticeship offers. Does it offer the variety of experiences that I had? Is industrial sponsorship as generous and altruistic as it once was? Do industry and government work hand in hand to ensure a future workforce has the skills that are needed?

Simply the answer is probably “no”. In fact, the structure and organisation of design and manufacturing organisations has changed dramatically. In aerospace there are some companies that have a major factory with every facility at their heart but most subcontract extensively. Colleges have been turned into educational shops, paid by student numbers.

Here’s a thought. It’s not so much what’s taught that’s key as much as the exposure to a variety of ways of thinking and working. A variety of exposure give a student a toolbox from which they can then draw. Finding interesting work will depend on adaptation and repurposing past skills. That’ll be the only way to assure the world doesn’t pass by at an ever-increasing pace.

I’m sure that advances in artificial intelligence (AI) will affect everyone[2]. The idea that all AI will do is displace people is wrong. It just means that, like my recollections above, the types of activities that needs to be done will be entirely different in 2065. Unless I’m highly unusual, I will be long gone. But if you are 25 years old this is worth a thought.

[1] https://archive.org/details/historyofprogram0000hist/page/n7/mode/2up

[2] https://nap.nationalacademies.org/download/27644#

The Revolutionary Role of Hydrogen

Hydrogen has a history with aviation. What could be better. A gas that is so light. So easily produced and with no need heat it up. With a lightweight gas-tight bag and a fair amount of rope, balloon construction took-off. Literally. The proof that hydrogen gas could lift a balloon goes back to the 1780s in France.

Sadly, the downside of this gaseous element is its propensity to combine with other elements. In fact, where would we be without liquid water. On this planet, that most basic and prolific combination of hydrogen and oxygen. Not so much sadly but more luckily.

Step forward about 250 years and we have a different vision for hydrogen in aviation. If it’s combined with the oxygen in the air that we breath, we get nothing more noxious than water. Since, the other forms of combustion, that populate our everyday lives, is distinctly noxious, surely hydrogen has a lot to offer. Talk about downsides. Burning fossil fuels is distinctly unsustainable. Polluting the atmosphere.

This week, I was looking out to sea. At the English Channel (No name changes there, I see). Standing on the pebble beach at Budleigh Salterton. They ought to have an award just for that name. It’s a small seaside town in Devon. The towns cliffs are part of a World Heritage Site, namely The Jurassic Coast[1].

Forget the 250 years of humans flying, cited above. About 185 million years of the Earth’s history is for all to see on the Devon and Dorset coast. When we say “fossil fuels” what we mean is that we are living off the back of Earth’s history. Society powers modern life on dinosaur juice. Well, not exactly but plant and animal life from hundreds of millions of years ago. How crazy is that?

Hydrogen, on the other hand, is one of the most abundant elements. It’s everywhere.

Modern day dinosaurs (politicians and pundits) insist that we continue to exploit dinosaur juice until it’s all gone. That’s putting aside any concerns about returning all that carbon to the Earth’s atmosphere. Carbon accumulated over millions of years.

Hydrogen can be a clean fuel. The problem is that saying that and then doing it are two different things. There are complexities that come with using Hydrogen as a fuel. It might be reasonably easy to produce, in multiple different ways, but it’s not so easy to transport.

Producing leak proof systems for transport and storage requires innovative thinking. We can’t just treat it with the familiarity of conventional fuels. Whole new regimes are going to be needed to get Hydrogen from where it’s produced to where it’s needed.

Producing leak proof systems for aircraft is a challenge. Given the odourless and invisible nature of this light gas, accurate and extensive detection systems are going to be needed. If the gas is to be consumed by fuel cells to produce electricity, then there’s going to be a constant struggle against complexity and significant expenditures.

What is reassuring is that none of the above is insolvable. At this time in history, we have the materials technology and control systems that make Hydrogen a viable clean fuel.

[1] https://jurassiccoast.org/

The Evolution of Air Traffic Control

Until civil air traffic started to grow the need for its control wasn’t the number one consideration. The pilot was the master of the skies. A basic “see and avoid” approach was taken. See another aircraft and avoid it at all costs. Note, I am talking about the early 1920s.

If you want a nice exploration of how it all started keep an eye on the site of the Croydon Airport Visitor Centre[1]. The first London airport was not Heathrow or Gatwick. No, there’s a stretch of grass, a hotel, industrial units and out of town shopping standing on the site in Croydon of the first London airport.

Firstly, we can thank Marconi for the first radiotelephony. Providing a means for pilots to speak to airports enabled the development of Air Traffic Control (ATC)[2]. It got going out of necessity because there was limited space on the ground and many aircraft wanted to take-off and land.

Aerial navigation took off in the 1920s. A hundred years ago. WWII drove advancement in every aspect of technology. After WWII, the basic having been established, an international body was established to set standards for international flying. That’s where today’s ICAO originated.

Radar and VHF radio transmissions were the cutting-edge technology that enabled air traffic to grow. Radio navigation aids developed as did automatic landing systems. So, by the time the jet-age started there was a whole selection of technology available to manage air traffic. Not only that but the standards required for these systems to interoperate around the globe were put down on paper.

That legacy has served aviation remarkably well. Incremental changes have been made as new capabilities have been developed. Most notable of that evolution is to return elements of control to the cockpit. A traffic alert and collision avoidance system (TCAS) does just that. It provides a safety net.

What we have available to manage dense airspace and busy airports is a complex, highly interconnected, interdependent set of systems of systems and procedures that is not easy to unravel. Each part, in each phase of flight, plays its role in assuring safe operations.

News and rumours are that quick fixes are being demanded in the US. Responding to recent accidents and a perception that all the above in antiquated, a well know tech guru has been thrown at the “problem”. I shouldn’t be a cynic, as having a fresh pair of eyes looking at the next steps in the development of air traffic management should be good – shouldn’t it?

It’s my observation, as an engineer who knows a thing or two about these things, is that any simple solution means that the parties have not thought long enough about the problem. In this case there are no quick fixes. However, there’s likely to be incremental improvements and they will not come cheap.

[1] https://www.historiccroydonairport.org.uk/opening-hours/

[2] https://www.historiccroydonairport.org.uk/interesting-topics/air-traffic-control/

Future of Single Pilot Operations in Aviation

Flying embraces automation. Now, there’s a statement that didn’t ought to be controversial, but it can be. Even before we became engulfed by the modern digital age, analogue autopilots could assist in the task of flying. Some early ones were mechanical.

The need for full-time hands-on piloting of the physical controls that linked a human and an aircraft’s control surfaces is not fundamental. Large transport aircraft have stepped further, somewhat mimicking what their military counterparts did, and fly-by-wire systems have become commonplace.

As far as technological evolution is concerned, we remain in a transitionary phase. Commercial aircraft that fly overhead are a mixed community. Some, like the Boeing 737 series continue to have cables and pulleys that link aircraft systems and controls. Others, like the Airbus A320 series are the fly-by-wire digital aircraft types in regular service.

Between the pilots in the cockpit and the motion of an aircraft there is a computer. In fact, several computers arranged in a manner so that they continue to work even when subject to failures. A great deal of thought and effort has gone into designing aircraft systems that will be reliable in-service.

Looking at the safety numbers, starting in the 1980s when fly-by-wire was introduced, the overall service experience is extremely good. The practice of system safety assessment has delivered dependable and robust aircraft. Rigorous certification processes are applied.

Through the technical developments that marched on from the 1980s one requirement has remained. That is that two pilots are needed in the aircraft cockpit. Granted there are exceptions to this rule for smaller transport aircraft. Single pilot operations are not new. For example, in many countries, the Cessna Caravan[1] is approved for a single pilot.

It’s 2025. It’s difficult not to notice the debate around Single Pilot Operations (SPO). That is to open large transport aircraft operations to a new rule. Lower operating costs may be achievable by making a change. It’s even said that this move is a way of continuing aviation’s growth as it becomes more and more difficult worldwide to increase the number of qualified pilots.

It’s good to see this subject being taken up in a forthcoming conference.

RAeS Flight Operations Conference 2025: Single Pilot Operations – Logical Progression or a Step Too Far?[2] 19 March 2025 – 20 March 2025. Royal Aeronautical Society Headquarters in London.

SPO may be enabled by use of complex systems to help make mission-critical decisions. The next step maybe with real-time “artificial” copilots and intelligent monitoring. Will this move the aviation industry toward safer and more efficient aircraft operations? That is the question.

[1] https://cessna.txtav.com/en/turboprop/caravan

[2] https://www.aerosociety.com/events-calendar/raes-flight-operations-conference-2025-single-pilot-operations-logical-progression-or-a-step-too-far

SONAR in Ocean Wreckage Recovery

Finding aircraft wreckage in the deep ocean is possible. However, it requires a degree of good fortune. Most of all, it requires the searcher to look in the right places. Lots of other factors come into play, particularly if the ocean floor is uneven or mountainous.

The primary tool for imaging the ocean floor is SONAR. That’s using the propagation of sound in water. SONAR can be of two types. One is called “passive” and the other called “active”.

The first case is like using a microphone to listen to what’s going on around. Of course, the device used is named appropriately: a hydrophone. It’s a device tuned to work in water and not air. Afterall, sound travels much faster in a liquid than it does in air.

Passive SONAR depends on the object of interest making a noise. Just like we have directional microphones so we can have directional hydrophones.

Passive SONAR is only useful if the aircraft wreckage is making a noise. Since in the case of Flight MH370, the battery powered underwater location beacons attached to the accident flight recorders have long since stopped working this kind of SONAR isn’t going to be much use.

Active SONAR is analogous to RADAR. That is where a pulse of high frequency sound is sent out through a body of water. Then sensitive hydrophones pick up a reflection of that pulse. It is detected and all sorts of miraculous digital signal processing is done with the acoustic signal, and an image is then formed. From that displayed image the human eye or sophisticated algorithms can make sense of what they are looking at on the sea floor.

Active SONAR can give both range and bearing (direction). Timing the sound pluses from their transmission to reception can give a way of calculating range. Or distance from the object providing a reflection. Bats know how to do this as they navigate the dark.

In sea water, there are complications. Sound does not always travel in a straight line in sea water. The speed of sound in water depends on salinity, temperature and pressure. All three of these factors can be measured and compensated for in the SONAR signal processing that I mentioned above. Helpfully at ocean depths beyond a kilometre the calculations become easier.

The average depth of the Indian Ocean is over 3 kilometres. It’s mountainous underwater too. So, what are the chances of finding flight MH370 on the ocean floor after 10-years[1]? This prospect goes back to my earlier comment. It requires the searcher to look in the right places.

Just imagine encountering the Grand Canyon for the first time. It’s nighttime. An important object is lost in the canyon. You only have the vaguest theories as to where the object has come to rest. With a handheld touch you go out to search. What are the chances of finding the object?

There are several factors that are in your favour. One, you know what the object might look like or, at least, in part. Two, the easy search locations (flat/smooth) may be covered relatively quickly. Three, certain areas of the rocky canyon have already been searched. Still the odds are against finding the lost object without a high degree of good fortune.

I wish the new planned searchers much good future[2].

NOTE 1: one of my student apprentice projects was to design and build a Sing-Around Velocimeter for use in relatively shallow sea water[3]. It worked but was cumbersome in comparison with the simple throw away devices used for temperature depth profiling.

NOTE 2: To get down to the ocean depths required it’s a side-scan sonar that may be used. This active sonar system consists of a towed transducer array that can be set to work at different depths. Imaging objects on the seafloor and underwater terrain is done as a towed array moves slowly forward through the water. The scanning part is the acoustic beam sweeps left and right. Each scan builds up part of an image.

In operation, as the frequency of the sound in water goes up so does the resolution of a potential image but, at the same time, the range of the sonar system goes down. Thus, a sonar system used for surveying may have low and high frequency settings. Unlike sound in air, here high frequency means above 500kHz.

NOTE 3: What will an aircraft accident recorder look like after a decade in the deep ocean? It might have survived well given the nature of the dark cold pressured environment. This picture is of an accident recorder recovered from relatively shallow sea water (Swiss Air Flight 111).

POST: Nice view of what SONAR can do, at least in shallow water Bristol Beaufort wreckage found

[1] https://www.cbsnews.com/news/mh370-plane-malaysia-new-search/

[2] https://www.bbc.co.uk/news/articles/cewxnwe5d11o

[3] https://apps.dtic.mil/sti/tr/pdf/AD0805095.pdf

Revitalising Manufacturing

Yes, it’s good to have good trading relations with other countries. With a degree of pragmatism – as many as possible. Naturally, there are lines drawn in cases where countries share little of the UK’s values or are dictator run aggressors. Counting the hundreds of sovereign countries there are around the globe, a majority are friendly and mostly interested in mutual wellbeing.

However, post-2016[1] we are still living in strange times in the UK. In the same breath as some people talk of sovereignty and surrender, they say an extremely wealthy man in the US can solve all the UK’s problems. This nonsense defies any kind of logic.

There’s a peculiar celebration of the UK joining the Asia-Pacific Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) bloc. As if we didn’t have a huge trading block on our immediate doorstep. Joining one that offers a tiny gain overtime whilst leaving the other has cost a massive economic hit. The one thousands of miles away is significantly culturally different but the one next door is one where we share a common history.

I learn that there’s no point even thinking that logic has any influence on a Brexit supporter. Non whatsoever. Their view of the world comes from some lost imperial age.

Sadly, Brexit talk is only mumbled in darkened corners. That whopping great elephant in the room continues to get ignored. Even the UK’s new Labour Government is carrying on as if there were the former Conservative bunglers. There’s some woolly talk of reconciliation. There’s a lot of right-wing scaremongering. Practically, not a lot is changing.

In real terms, both UK exports and imports of goods are lower than in 2016, having shrunk by 1% and 2%, respectively[2]. Which is crazy given the new economic horizons. Especially in the switch to the need for more environmentally responsible goods. We should be modernising and strengthening UK design and manufacturing. Not just a bit but putting a rocket under both. Half hearted nice words by minor Ministers don’t cut it.

International trade fantasies will not build a stronger domestic economy and that illusive positive growth that’s often talked about in political speeches. With the coming of highly advanced computing, like artificial intelligence, countries with predominantly service based economies are gong to struggle. Basic service orientated jobs are going to get more automated. Like the traditional factories Henry Ford would have recognised, office complexes are hollowing out.

At least the new Labour Government isn’t pushing wholesale reopening coal mines or returning to a dependency on North Sea oil rigs. That said, I’m unsure what their attitude and policy is to rock fracking and imported gas supplies.

To make real economic progress we (UK) must make Brexit history. With our colleagues in Europe, we can be an innovation powerhouse. Making home grown products for the world markets of the future. Not languishing in a tepid imperial past or tugging at the shirt tails of some mega weird pugilist.

[1] UK referendum result: Of those who voted, 51.89% voted to leave the EU (Leave), and 48.11% voted to remain a member of the EU (Remain).

[2] https://personal.lse.ac.uk/sampsont/BrexitUKTrade.pdf

H2 Aircraft Design

Cards on the table. I’m a believer. Despite the immense technical challenges, Hydrogen is a viable fuel for future large civil aircraft. That said, operational service of such revolutionary aircraft isn’t going to happen in a hurry.

Reading the history, Concorde was an incredible test of the boundaries of what was possible and that was met, but it didn’t come easy. Breaking new ground is never easy. [A common saying that’s maybe open to challenge]. In aviation making step-changes happens every decade. What’s nearly always required is exceptional determination, almost beyond reason, large sums of money and special people.

Control systems – no big deal. Mechanical components – evolution possible. Turning a gaseous fuel into high-levels of propulsive thrust – can be done. Building a one-off technology proving research vehicle. It’s happening. At least for the light and commuter class of aircraft.

None of this is enough. Because the gap between an aircraft that can fly and an aircraft that can be produced in the thousands and go on to make an operational living and build an impressive safety and reliability reputation, that’s still a million miles off.

Today, there’s artist impressions of all sorts of different H2 aircraft configurations. It’s like people painted pictures of Mars with imaginary canals, long before anyone knew what the planet looked like in reality. Innovation starts with ideas and not all of them are sound.

As I expressed in my last article, crashworthiness must be given much consideration when speculating about future designs. It’s not always explicit in aircraft certification, cabin safety being the exception, but studying the history of accidents and incidents is essential. One of the successes of the authorities and industry working together is to take lessons learned seriously.

I remember looking at the pictures of the wreckage of Air France Flight 358, which crashed on landing in Toronto, Canada[1]. The fact that there were no fatalities from that accident is a testament to good operations and good design practices. The Airbus aircraft burned out but there was enough time for passengers and crew to get away.

My thought is what kind of H2 aircraft configurations would permit the same opportunity?

Considering this large aircraft accident, and others like it, then there’s a message as to where fuel tanks might best be placed. There’re some aircraft configurations that would have little hope of providing the opportunity for rapid evacuation of hundreds of people.

So, in my mind, don’t attached large pressurised cryogenic fuel tanks to the underbody structure of an aircraft fuselage. However robust the design and build of such fuel tanks they would be unlikely to survive as well as the cabin passenger seats, namely 9g[2]. That would not provide a good outcome post-accident.

Maybe, like aircraft engines sitting on pylons off the wings, that too is a good place for fuel tanks.

[1] https://asn.flightsafety.org/asndb/322361

[2] https://www.easa.europa.eu/sites/default/files/dfu/NPA%202013-20.pdf

Challenges of Hydrogen Fuel in Civil Aviation

This week has been a Hydrogen week. It’s great to learn more of the projects that are out there and the ambitions of those developing systems. Hydrogen is a live subject. Looking at the possible pathways for civil aviation to take there’s a myriad of choices. However, when it comes to the fuel for propulsion there are not so many potentials.

It’s surely the case that at some time in the future the use of fossil fuels to propel us across the skies will no longer be acceptable. Even if I’m talking to climate change sceptics the point must be made that fossil fuels are a limited resource. Not only that but the air quality around airports is a matter of concern.

It’s there in our basic education. Water is H₂O. It’s that combination of Hydrogen and Oxygen that is essential to life on Earth. So, if we have a process that provides aircraft propulsion by using Hydrogen it should be a whole lot better for the environment than using Jet A1.

The problem is, and there’s always a problem, to carry enough Hydrogen it will need to be pressurised and in liquid form. That means extremely low temperatures, robust storage containers and extensive leak free plumbing.

Today, we have cars on the road that run on liquefied petroleum gas (LPG). It’s a novelty. It’s less harmful to the environment and can cost less. However, LPG systems need regular servicing. The point of mentioning this pressured gas in a transport system is that it has been integrated into regular everyday usage. That’s knowing that escape of even small quantities of the liquefied gas can give rise to large volumes of gas / air mixture and thus a considerable hazard[1].

Any analogy between the car and the aircraft can be forgotten. That said, one or two of the issues are similar. Yes, what happens when an escaped volume of gas / air mixture is ignited?

What scenarios would bring about conditions whereby a destructive explosion is possible?

Let’s start with the situations where aircraft accidents most often occur. Take-off and landing are those phases of flight. A surprising number of accident scenarios are survivable. The important part being to get an aircraft in trouble on the ground in such a way that an evacuation is possible. That can mean hitting the ground with a great deal of force[2].

Here’s the matter of concern. An aircraft with large cryogenic tanks and associated complex plumbing hits the ground at a force of many “g”. What then happens? Certainly, pressurised liquefied gas would escape. Being a very light gas, the uncontained Hydrogen would rise rapidly. However, trapped amounts of gas / air mixture would remain a hazard. Would that be ignited?

There are a lot of unknowns in my questions. Although there are unknowns, any post impact situation is likely to be very different from a situation with a conventionally fuelled aircraft.

Today’s, burn through requirements ensure that an external fuel fire is held back. Thereby ensuring enough time to evacuate. For a hydrogen aircraft ventilation may be essential to stop build-up of a gas / air mixture inside a fuselage. That means a whole different approach.

[1] https://youtu.be/AG4JwbK3-q0

[2] https://skybrary.aero/accidents-and-incidents/b772-london-heathrow-uk-2008