Tag: Aviation

Upfront

Years of looking at the reliability of aircraft components and structure have given engineers a good understanding of the natural decay of mechanical workings. To that extent even electronic components are mechanical. Materials oxidise (rust), random shocks and vibration take their toll, temperatures cycles from cold to hot and back again a whole range of impacts are relentless. You can say – nothing lasts forever.

Occasionally a discovery adds to the knowledge of how materials behave under high stress. Sadly, that’s what hit the early years of civil jet aviation. The de Havilland DH106 “Comet” was the world’s first passenger carrying jet airliner. It first took to the air in 1949, which I find remarkable.

Catastrophic metal fatigue failure of the aircraft fuselage put paid to this British aviation project but only after several tragic fatal accidents. In 1954, the Comet aircraft were all grounded during an extensive accident investigation. The jets were redesigned and re-entered commercial service in 1958. However, by then the aircraft had a damaged reputation and others were doing far better. Now, those Comet aircraft that remain are museum exhibits[1].

Last week, I walked through the fuselage of a Comet 1A built in 1953 at Hatfield for Air France. It’s fascinating to see what advanced aviation technology was 70-years ago. What was surprising to me was the read across from that first version of a jet aircraft and what we have in-service now.

Automation has removed the place of the navigator and the flight engineer, but the stations of the pilot and co-pilot are familiar. The fuselage is cramped but the seating is generous and spacious. This aircraft must have been a dramatic revolution in flying at the time.

As we look to advance aviation in the coming years, with new ways of flying and new ways of powering flight so the warning of the Comet project should be heeded. We are at a time of extraordinary changes in the aviation industry. Advanced technology can deliver great benefits to society. It’s up to us to make sure we cover all the possible disbenefits as far upfront as we can. If we don’t, they will come back to bite us.

[1] https://www.dehavillandmuseum.co.uk/aircraft/de-havilland-dh106-comet-1a/

Learn by testing

Back in the mid-1980s, aircraft system integration was part of my stock-in-trade. Project managing the integration of a safety critical system into a large new helicopter. It was a challenging but rewarding job. Rewarding in that there was a successful new aircraft at the end of the day.

For big and expensive development projects there are a great number of risks. The technical ones focus on functionality, performance, and safety. The commercial ones focus on getting the job done on-time and at a reasonable price. Project managers are in the middle of that sandwich.

Naturally, the expectations of corporate managers in the companies that take on these big challenges is that systems and equipment integration can be done to the book. Quickly and without unexpected outcomes. The practical reality is that people must be well prepared and extremely lucky not to encounter setbacks and resets. It’s not just test failures and anomalies that must be investigated and addressed. Systems integrators are working on shifting sand. The more that is known about overall aircraft flight test performance and customers preferences so technical specifications change.

With cockpit display systems, in the early days, that was often feedback from customer pilots who called for changes to the colour, size or shape of the symbology that was displayed on their screens. What can seem a simple post-flight debriefing remark could then turn into a huge change programme.

That was particularly true of safety critical software-based systems. Equipment suppliers may have advanced their design to a state where much of the expensive design validation and verification was complete. Then a system integrator comes up with a whole set of change that need to be done without additional costs and delivered super-fast. Once a flight test programme gets going it can’t be stopped without serious implications. It’s a highly dynamic situation[1].

I’m writing this blog in reaction to the news coming from Vertical Aerospace. Their VX4 prototype aircraft was involved in an flight test incident that did a lot of damage[2]. There’s no doubt this incident can provide data to feedback into the design, performance, and safety of future versions of their aircraft[3]. Integrating complex hardware and software is hard but the rewards are great.

“Excellence is never an accident. It is always the result of high intention, sincere effort, and intelligent execution.” – Aristotle

[1] https://youtu.be/Gb_eta4mZkc

[2] https://evtolinsights.com/2023/08/vertical-aerospace-identifies-propeller-as-root-cause-of-august-9-vx4-incident/

[3] https://investor.vertical-aerospace.com/news/news-details/2023/Vertical-Aerospaces-VX4-Programme-Moves-to-the-Next-Phase/default.aspx

NATS

A “technical issue” has caused UK National Air Traffic Services, NATS to impose air traffic flow restrictions[1]. They did not close UK airspace. This was not a repeat of the volcanic ash events of early 2010. Going from a fully automated system to a fully manual system had the dramatic impact that might be expected. The consequences, on one of the busiest weekends in the holiday calendar were extremely significant. Huge numbers of people have had their travel disrupted. Restricting the air traffic system ensured that aviation safety was maintained. The costs came to the UK’s air traffic handling capacity and that meant delays and cancelled flights.

Although the failures that caused the air traffic restriction were quickly resolved the time to recover from this incident meant it had a long tail. Lots of spoilt holidays and messed up travel plans.

It is normal for an Air Traffic Service (ATS) provider to undertake a common cause failure analysis. This is to identify multiple failures that may result from one event. So, the early public explanations coming from NATS of the causes of this major incident are surprising. Across the globe, contingency planning is a requirement for ATS. The requirement for the development, promulgation and application of contingency plans is called up in international standards, namely ICAO Annex 11.

So, the story that a single piece of flight data brought down the traffic handling capacity of a safety related system, to such a low level, is difficult to accept. It’s evident that there is redundancy in the systems of NATS, but it seems to be woefully inadequate when faced with reality. ATS comprise of people, procedures, and systems. Each has a role to play. Safety of operations comes first in priority and then air traffic handling capacity. What we know about even highly trained people and data entry is that human error is an everyday issue. System design and implementation needs to be robust enough to accommodate this fact. So, again attributing such a highly disruptive event to one set of incorrect data inputs does not chime with good practice or basic aviation safety management. It is concerning that one action can bring down a major network in this way.

EUROCONTROL would have had been sent a “rogue” flight plan in the same way as UK NATS. Brussels does not seem to have had the problems of the UK.

It is early days in respect of any detailed technical investigation. Drawing conclusions, whatever is said in public by senior officials may not be the best thing to do.

Calls for compensation have a good basis for proceeding. The holiday flight chaos across Europe comes down to one single failure, if initial reports are correct. That can not be acceptable. The incident left thousands stranded abroad with high costs to pay to get home.

Before privatisation, there was a time when the UK Civil Aviation Authority (CAA), ran the nation’s air traffic services[2]. It had a poor reputation at the time. I remember a popular newspaper cartoon saying – and now for some clowns from the CAA. They were entertaining delayed passengers.

UK NATS has done much good work to manage a safe expansion in air traffic and address many changes in technology, it would be a shame if this sad incident marks a decline in overall network performance.

NOTE 1: And this topical cartoon from the Daily Mail in April 2002: https://www.pinterest.es/pin/497577458805993023/

NOTE 2: A report on the incident is to be sent to the regulator, UK CAA on Monday, 6th September. Transport secretary to see Nats’ ATC meltdown report next week | Travel Weekly

NOTE 3: The likelihood of one in 15 million sounds like a low number but it’s not “incredibly rare” by any definition. Certainty when there are around 6000 flights a day in the UK. A duplicate error occurring is a basic error that could be anticipated.

[1] https://www.bbc.co.uk/news/live/uk-66644343

[2] https://commonslibrary.parliament.uk/research-briefings/sn01309/

Even more H2

There’s a couple of Hydrogen related topics that are worth a moment. One is super conductors and the other is fire.

Heavy complex equipment like the magnets for particle accelerators use superconductors[1]. When there’s space and a need for powerful magnetics, materials with special physical properties, at extreme cold temperatures find a good use.

Talk of room-temperature superconductors is far from what it seems. Such a wonderful innovation is a million miles from any practical applications, if it exists at all. There’s no theory of high-temperature superconductivity, but there’s quite a few physicists who would like to find one[2].

Aviation researchers search for high temperature superconductors for electrical propulsion with extraordinary performance is on. The likelihood of success is low, and the timeframes are very long.

When an aircraft is flying at high altitude, the cabin altitude is maintained for the safety and comfort of passengers and crew. Air compressors, valves, sensors, and controllers make sure that cabin pressure remains at equivalent to an altitude of about 8,000 feet, and lower in some cases. So, any kind of simply flammable gasses or materials inside an aircraft cabin are a definite no no. It’s a big hazard.

In flight, the positive pressure should keep leaking gas out of the cabin. That is as long as the sources of fresh air for the cabin are keep well away from potential leaks.

That’s where Hydrogen gas can present trouble. Leaks can be common in dynamic Hydrogen systems. Storage tanks must be very strong to resist pressures and insulated to keep cold, at around –250°C. Escaping H2 gas is tiny. If that’s vented overboard then the risk of explosion or fire is significantly lowered. Knowing the exact flows of liquid or gas is a must.

However, if the gas finds its way into a pressurise cabin that basic option is limited. Not only that but detecting low concentrations of the gas in the first place is mighty difficult. Its odourless but at least Hydrogen isn’t poisonous.

The big safety issue is that the gas has a very wide flammability range (4 – 70% H2 in air mixture)[3]. Yes, H2 needs a spark to ignite. A typical aircraft cabin environment will easily provide that event. Dry air and static electricity will do it even if other sources will not.

To compound difficulties, if H2 does ignite, and not explode, then its flame may not be visible to the human eye. The flame is almost colourless. Certainly, not what most people think of as a gas flame. Gas and flame detectors could be installed in aircraft cabins and baggage compartments. Audible and visual alarms could be generated but what would be the associated crew actions?

All the above requires detailed consideration in aircraft safety assessments. The move away from prescriptive regulatory requirements means each specific aircraft configuration must be addressed. There are no generic lessons to learn from past aviation accidents and incidents.

Although, I think these puzzles can be solved it’s a huge leap from here to there.

POST: Yes, Hydrogen is not for every application. Small scale aviation is better served by electrification Five Hydrogen Myths – Busted. – RMI

[1] https://home.cern/science/engineering/superconductivity

[2] https://www.science.org/doi/epdf/10.1126/science.adk2105

[3] https://h2tools.org/bestpractices/hydrogen-flames

More H2

I think this came at me both ways as a schoolboy. Both from chemistry and physics. In our 1960s chemistry lab, Bunsen burners, flasks and array of hazardous substances were the norm. Physics seemed more cerebral. Still, the hands-on side of teaching still meant some practical experimentation. That’s the part that most engrossed me.

Electrolysis starred in two mostly harmless experiments. The colourful one was about copper sulfate[1] and the other was about splitting water into its component parts. Getting Oxygen (O2) and Hydrogen (H2) gas by electrolysis[2] is mighty simple and one of those wonders of nature.

Electrolysis is a way of producing carbon-free Hydrogen from renewable and nuclear resources. Despite the apparent straightforwardness of the process, it’s quite tricky to industrialise on a large scale. One key factor to the future use of Hydrogen is getting the cost per Kg down[3].

Let’s presume that this is a solvable problem and cheap and plentiful gas supplies will be up and running by 2030. That’s not so far off given its 2023. There will surely be a market for ample supplies given the multitude of applications for Hydrogen. Will it be a global market? It needs to be.

It’s a talking point. Hydrogen fuel is one of the viable fuels for aviation. Generating power and returning it to water in the atmosphere is an attractive idea. The process meets carbon-free ambitions even if it does have lots of complications.

On average, a Boeing 737-800 uses about 5,000 lbs (2268 kg) of conventional fuel per flight hour[4]. Cryogenic Hydrogen has lower energy density. That means much more on-board fuel storage will be needed to go as far or fly as long as a current day common commercial jet aircraft.

Designing an aircraft configuration that can accommodate these facts can be done but what of the space that remains for the payload? As it does today, on-board fuel storage will need to meet stringent safety requirements.

Adding this up, it may not be the technical issues that make this difficult. Although they are difficult the technical issues can be addressed. However, will the overall package that results be economically viable? If costs are increased by a factor of, say 5, will this provide for a commercial air transport system that is like the current one?

We may have to accept that carbon-free flying reverts to the 1960s[5]. What I mean is that, instead of low-cost flights hopping here, there, and everywhere for £100, the future maybe one where long-haul flying is a relative luxury or an expensive business need.

[1] https://www.bbc.co.uk/bitesize/guides/zgn8b82/revision/3

[2] https://www.bbc.co.uk/bitesize/guides/zv2yb82/revision/1

[3] https://www.statista.com/statistics/1220812/global-hydrogen-production-cost-forecast-by-scenario/

[4] http://www.b737.org.uk/fuel.htm

[5] https://www.skyscanner.com.au/news/airlines/the-golden-age-of-plane-travel-what-flying-was-like-in-the-1950s-and-1960s-compared-to-now

Electric Flight

Hype has its place. Being positive while buffeted by the inevitable ups and downs of life is purposeful and necessary. What’s not true, and might be the impression, is that electric aviation is easy. When forging ahead to build a future, that is not yet realised, there’s a need to maintain confidence. However, being blinded by the light doesn’t help when it comes to tackling difficult problems. Proof-of-concept is just that.

The big positives of electric aviation are the environmental benefits. Electric aviation is spawning many new types of aircraft and the possibilities of new types of operation. So, there’s no doubt that this is an exciting time to be an aviation enthusiast. What a great time to be in aerospace design and manufacturing. Here we are at the start of a new era[1].

My point is that high power electrics, and their control are not “simple” or intrinsically safe in ways other types of aircraft are not. I know that’s a double negative. Better I say that high power electrics, operated in a harsh airborne environment have their own complexities, especially in control and failure management. Fostering an illusion that the time between having an idea and getting it into service can be done in the blink of an eye is dangerous.

The design, development and production of advanced aircraft power distribution, control and avionics systems is not for the faint hearted. Handling large amounts of electrical power doesn’t have the outward evidence of large spinning mechanical systems but never underestimate the real power involved. Power is power.

The eVTOL aircraft in development deploy innovative design strategies. There’s a lot that’s new. Especially all together in one flying vehicle. Everyone wants fully electric and hybrid-electric aircraft with usable range and payload capacity. So, the race is one. Companies are productising the designs for electric motors of powers of greater than 10kW/kg[2] with high efficiency and impressive reliable. These systems will demand suitable care and attention when they get out into the operating world.

A 500kW motor will go up with one hell of a bang and fire when it fails. The avionics may shut it down, but everything will have to work smoothy as designed every day, not just in-flight but on the ground too. Suppressing an electrical fire isn’t the same as a conventional fuel fire either. To fix these machines the care needed will be great. 1000 Volt connections capable of supplying high power can kill.

Not wishing to be focussed on the problems but here I go. Another major problem is the number of qualified engineers, with knowledge and experience who can work in this area. The companies who know how to do this demanding work are desperately searching for new people to join their ranks.

Educators are starting to consider these demands as they plan for the future. Sadly, there’s not so many of them across the globe who are so foward looking.

The global aviation industry needs to step-up and train people like crazy. The demand for Subject Matter Experts (SMEs) is self-evident. That’s true in design, production, and maintenance. Post COVID budgets maybe stretched but without the big-time investments in people as well as machinery success will be nothing but an illusion.

POST1 : Or 150 kW motors when you have many of them going at once. Rolls-Royce Electrical Testing eVTOL Lift Motor | Aviation Week Network

POST 2: Getting ready Preparing Your Airport for Electric Aircraft and Hydrogen Technologies | The National Academies Press

[1] https://smg-consulting.com/advanced-air-mobility

[2] https://www.electricmotorengineering.com/h3x-new-investments-for-the-sustainable-aviation/

Pathway

Conversation drifts across a table. “What do you do?” It’s a classic conversation starter. Maybe “Where are you from?” comes up just as often. It’s those basics about identity that either bond us together or throw us apart. Or at least tigger certain ingrained responses.

In a society, like ours that has a long tail of class-based judgement, these questions have greater implications than elsewhere. In of itself that is a questionable remark. Leave the UK and similar markers create stereotypes that are easily recognisable. US comedy is full of them. For fans of the classic series like MASH[1] or Frasier[2] they are there is spades. Situation comedy often depends on misunderstandings and social tensions.

Anyway, I’m writing this when it comes to mind what a big gulf there is between those of us who had “desk jobs” and people who worked far more with their hands and wits. The labels of administrator or artisan can be stamped out so easily in British society.

A conversation went like this – I was a coach builder. I built lorries. I could never have done a desk job. My response was – I was lucky. Sometimes, I sat at a desk under piles of paper. Or in front of a keyboard. Sometimes, I travelled to, just about anywhere, where they built or flew aircraft and got to deal with real hardware. But however much there was an overlap between us two seniors at a bar, there was still a gulf that was probably born of a dividing line that was drawn when we were teenagers. Streaming people away from academic study was a grading system, certainly in the 1970s.

You might say that these traditional social barriers are a thing of the past. They are not, are they? In fact, in powerful places the line between people with real lived experience in craft or public service type roles is growing. Take a cross section of Members of Parliament. How many can count an experience of working a skilled trade or hands-on time doing something useful?

The Oxbridge mafia is as in control as it ever has been. Although recent examples from that background should be enough to put people off. The leisurely stroll from Philosophy, Politics and Economics (PPE) to the green benches is so much simpler than any other pathway.

I love the revitalisation of apprenticeships[3]. However, that word now means something different from what it once did. There weren’t such notions as intermediate or advanced apprenticeships in my time, although they were implicit. Just a few found a sponsor and a pathway to a degree course on the same level as those who stayed on at school.

As much as providing new pathways the social context still matters. Elevating the status of apprenticeships matters. This is a first-class stream. From it can come future leaders.

[1] https://www.imdb.com/title/tt0068098/

[2] https://www.imdb.com/title/tt0106004/

[3] https://www.bbc.co.uk/bitesize/articles/z4n7kmn

H2 is difficult

I mentioned Hydrogen as an option for aviation. The use of Hydrogen to either power jet engines or to power fuel cells to provide electricity is a real technical option. Although the person I was talking to was engaged in environmental work, they shrugged their shoulders when I mentioned Hydrogen. They were certainly not impressed by these possibilities despite our agreement on the urgent need for de-carbonisation.

I can understand why there’s a level of cynicisms. On my part, it’s like the X-Files[1]. Fox Mulder was the believer and Dana Scully the sceptic. Broadly, I want to believe.

Today’s, liquid fuels can be explosive in certain conditions. However, it takes a considerable effort to create the conditions whereby a devastating explosion can occur. The Boeing 747-100 that was Trans World Airlines Flight 800 (TWA 800)[2] exploded, broke up in the air and fell into the Atlantic Ocean in 1996. This was an example of a worst-case scenario. 230 people were lost in that fatal accident. Now, the ignition of a flammable fuel/air mixture in aircraft tanks is better prevented by design and operational procedures.

If Hydrogen is to be viable in civil aviation such hazardous conditions will be harder to prevent. A flammable hydrogen/air mixture can be ignited much more easily than conventional liquid fuels. Such dangerous situations can be prevented but the measure to do so will require robust design and stringent operational procedures.

Several development programmes are underway, making practical Hydrogen powered aircraft viable. A range of aircraft configurations are possible. From hybrid generator and electric motor set-ups to combustion-based propulsion. This work is moving from academic research into commercial possibilities.

There little read across between the behaviour of conventional hydrocarbon liquid fuels and liquid Hydrogen. This would be evident in any serious incident or accident scenario. Let us imagine the case of British Airways Flight 38, in 2006, a Boeing 777-236 that came down at the end of a runway at London Heathrow[3]. A significant amount of fuel leaked from the aircraft after it came to rest, but there was no fire. There were no fatalities.

The breakup of liquid Hydrogen tanks or plumbing in such a scenario would almost certainly result in a significant fire. The mitigating impact of that fire is the lightness of the gas. Instead of liquid fuel pooling on the ground, Hydrogen would burn upward. However, any explosion could be devastating.

So, for large aircraft design the provisions to protect liquid Hydrogen tanks and plumbing must be extensive and extremely robust. This would have to be maintained, as such throughout the whole operational life of the aircraft. These requirements would be onerous.

Keeping crew and passengers well away from Hydrogen infrastructure will be a must.

POST 1: Crashworthiness doesn’t get much of a look-in. Without it there’s going to be a problem over the horizon. https://www.ati.org.uk/flyzero-reports/

POST 2: At least for eVTOL aircraft some work is being done. https://ieeexplore.ieee.org/document/10011735

[1] https://www.imdb.com/title/tt0106179/

[2] https://www.history.com/news/twa-flight-800-crash-investigation

[3] https://assets.publishing.service.gov.uk/media/5422ec32e5274a13170000ed/S1-2008_G-YMMM.pdf

Local air

There are cases of synergy. That’s where aviation and local authorities have a mutual interest. This often centres around the economic prosperity of an area. Relationships can be complex, difficult, and fraught with volatility. There are plenty of housing and industrial estates that cover the ground of former airfields. Like the railways that closed under Beeching’s axe[1].

Public interest was dominant 50-years ago, but privatisation dramatically changed relationships. Sustaining profitability through good times and bad have proven to be more than some locations could support. There’s so many combinations and permutations but fewer and fewer active commercial airfields in the UK.

London Manston Airport is an airport that only just clings on to existence. In 2013, the Welsh Government acquired Cardiff Airport. So, some aviation facilities have returned to public ownership and run as an arm’s length business. A few airports are given support to ensure connections exists between remote parts of the UK. Highlands and Islands Airports is an example.

Advanced Air Mobility (AAM) is coming. This is the extensive use of electric vertical take-off and landing aircraft (eVTOLs). AAM is an innovative concept that will require Vertiports and integration into busy airspace. To make the economics work a lot of routes will be in, and over urban areas.

My view is that AAM will only succeed in the UK if aviation and local authorities come together and embrace it. That is going to be a massive challenge whatever national government does.

In the case of local authorities with a mission of protecting the interests of residents this has often meant objecting to aviation developments. I go back to proposals of 30-years ago to make Redhill Aerodrome a feeder to London Gatwick Airport[2]. This was well and truly shot down by local interests. In fact, rightly so given the complex twists and turns it would have made in the airspace.

AAM needs the harmonisation of standards to ensure interoperability anywhere in the country. There are one or two UK local authorities that are already embracing the potential opportunities of this new form of flying. Coventry City Council is taking on the challenge[3]. It’s welcoming the development of the ground infrastructure for “air taxis” and delivery drones.

By the way, my view is that introducing the subject as “flying cars” or “air taxis” is not a good idea. This creates images from science fiction that may not resemble the reality of these new air services.

[1] https://www.networkrail.co.uk/who-we-are/our-history/making-the-connection/dr-beechings-axe/

[2]https://john-w-vincent.com/wp-content/uploads/2023/08/bf3ec-clear_for_take_off.pdf

[3] https://www.coventry.gov.uk/news/article/4232/world-first-hub-for-flying-taxis-air-one-opens-in-coventry-uk-heralding-a-new-age-of-zero-emission-transport

Weight

Projects aiming to electrify aviation are numerous. This is one strand to the vigorous effort to reduce the environmental impact of civil aviation. Clearly, feasible aircraft that do not use combustion are an attractive possibility. This step shows signs of being practical for the smaller sizes of aircraft.

Along the research road there are several hurdles that need to be overcome. One centres around the source of airborne power that is used. State-of-the-art battery technology is heavy. The combinations of materials used, and the modest power densities available result in the need for bulky batteries.

For any vehicle based on electric propulsion a chief challenge is not only to carry a useful load but to carry its own power source. These issues are evident in the introduction of electric road vehicles. They are by no means insurmountable, but they are quite different from conventional combustion engineered vehicles.

The density of conventional liquid fuels means that we get a big bang for your buck[1]. Not only that but as a flight progresses so the weight of fuel to be carried by an aircraft reduces. That’s two major pluses for kerosene. The major negative remains the environmental impact of its use.

Both electricity and conventional liquid fuels have a huge plus. The ground infrastructure needed to move them from A to B is well understood and not onerously expensive. It’s no good considering an aircraft design entirely in isolation. Any useful vehicle needs to be able to be re-powered easily, not too frequently and without breaking the bank[2].

Back to the subject of weight. It really is a number one concern. I recall a certain large helicopter design were the effort put into weight reduction was considerable. Design engineers were rushing around trying to shave-off even a tiny fraction of weight from every bit of kit. At one stage it was mooted that designers should remove all the handles from the avionics boxes in the e-bay of the aircraft. That was dismissed after further thought about how that idea would impact aircraft maintenance. However, suppliers were urged think again about equipment handling.

This extensive exercise happened because less aircraft weight equated to more aircraft payload. That simple equation was a massive commercial driver. It could be the difference between being competitive in the marketplace or being overtaken by others.

Aviation will always face this problem. Aircraft design is sensitive to weight. Not only does this mean maximum power at minimum weight, but this mean that what power that is available must be used in the most efficient manner possible.

So, is there a huge international investment in power electronics for aviation? Yes, it does come down to semiconductors. Now, there’s a lot of piggybacking[3] from the automotive industries. In my view that’s NOT good enough. [Sorry, about the idiom overload].

[1] https://dictionary.cambridge.org/dictionary/english/bang-for-the-buck

[2] https://dictionary.cambridge.org/dictionary/english/break-the-bank

[3] https://dictionary.cambridge.org/dictionary/english/piggybacking