Flight MH370 MAS

In the past few days we have been beset with much grief – again.

Why?

Because another aircraft is missing with people on board.

There are many people aboard this aeroplane but, in real terms it matters little if there are five hundred or there is only one person. It is a matter of scale and the quantity of grief with which the World becomes awash.

Let us stop, just for a moment, and consider a couple of things here.

Firstly we should look at that third sentence. It says that an aircraft is missing.

Say that again slowly, ‘an aircraft is missing.’

Notice that, at the end of the sentence, there is a full stop. It is at precisely this point that the conversation should stop. Anything said after that is conjecture, it is speculation; there is no place in aviation for that. None.

When we get to that full stop we say, in our heads, that ‘we don’t know’ what happened. And that part is the truth. We do not know.

Shall we move on to a headline. It is dramatic, it is sensational. It shouts at us that ‘Terrorism Suspected in Missing Flight’.

This is guessing. It is speculation. There is absolutely no evidence to support this idea. That there are people flying on the aircraft with stolen passports is no indication of terrorism at all. There are a thousand reasons – well, several, anyway, why someone should be flying with a stolen passport and terrorism is not one of them.

We have ‘International Terrorism’ stuck in our heads by the media who are so anxious that there should be ghouls and ghosties behind every headline.

Consider this: there are only three questions ever asked by the news media. They are:

1.                  How bad is it?

2.                  How bad can it get?

3.                  What can be done about it.

They never, ever, ask about the good news.

These guessing games played by the news are no comfort to the friends and families of those who are missing. It is much better to say nothing, or pray for them if you will, than go on these wild crusades.

We hope that, ultimately, they will find the FDR (Flight Data Recorder – the ‘Black Box’) and the CVR (Cockpit Voice Recorder so that the truth may finally reveal itself to us.

Until then all else is conjecture. It is rumour, hearsay and, mostly, nonsense.

Let us not spread it around. Even if only for respect.

Thank you.

ADDENDUM

With reference to my ‘Blog’ of Monday, June 17, 2013.

The publisher is happy to announce that the problem with the postage rates has been resolved.

Copies of ‘A Simple Guide To Understanding Jet Engines’ are now available from ‘Amazon’ in the United States, the United Kingdom as well as Germany and France.

Thank you for your patience; we hope that this has not resulted in any problems or anguish for those studying for their EASA* or FAA* Pilot’s, Engineer’s or Mechanic’s licenses.

*NB: Also applicable to CAAS, CASA, Transport Canada, DCA(M), CAAC, etc.

Billions of US Dollars Wasted

For the uninitiated I should like to point out that working on, near or around aeroplanes is dangerous.

As I am fond of telling the participants on my courses the statistics do not support a long and healthy life.

Ground incidents are reported to be costing commercial airlines in the region of USD10 Billion a year.

Ten Billion.

We have no concept of what a ‘Billion’ is. We will, for the moment anyway, stick with the devalued American ‘Billion’ that is One Thousand Million. A British Billion is One Million Million.

It is impossible to imagine one billion. Our brains just will not encompass such a number. We think we know but we do not.

In fact, our brains have problems with any number greater than, say, seven!

When the Americans announced that there was trade deficit of three trillion dollars—yes, dear heart, three trillion dollars, everybody tutted and shook their heads.

If they had said that there was a trade deficit of one hundred and forty five dollars and ninety cents there would have been uproar. Why? Because we can imagine smaller numbers; we know what they will buy; we are accustomed to smaller numbers.

Three Trillion? No chance.

Humour me, do a small exercise. Get your mobile ‘phone or iPad—or what you will, out and tell me what you were doing one billion seconds ago.

Got it?

Surprised?

Now lets go back to the original thought.

Ground incidents are said to be costing Ten Billion US Dollars EVERY YEAR!

The figure rises.

Every single incident is avoidable. Every single incident is the result of someone:

Thinking that they know what they are doing,

Thinking someone else knows what they are doing,

Not thinking!

Everybody has had training. Every single person that goes near an aeroplane has had some instruction about safety.

Everybody.

Statistics may be scoffed at but they do not lie. We know, for example, that people get sucked into jet intakes. They die. Yes, we have all heard the stories—maybe even seen the video where a guy goes down an intake and survives. A rarity.

Every one else dies.

When you go down a jet intake the depression that was there already now gets worse because your body is creating an obstruction to the airflow. The engine is still ‘sucking’ for all it is worth.

Your lungs will empty and then they will try to rip out of your body resulting in your death by drowning—in your own blood. If you are lucky the engine will chop you into tiny pieces

Yes, it is sickening. It is extremely unpleasant but it is a fact. It is what happens if you stop thinking for a moment. This guy was highly experienced; he was 64. 

How many people get struck by propellers, tail rotors on helicopters, main rotors, ground support vehicles?

Many.

The cost in human terms is tragic. The friends and family now enter a period of great sadness known as ‘mourning’; Husband, Dad, Friend is gone.

We have said that these are incidents but we know that there is a difference between incidents and accidents.

It is the combination of these that costs so much.

We have rules, regulations, laws, checklists and training for a reason.

The reason is to keep you safe.

What are my ‘Aviation Maintenance Rules’?

Rule 1: Look after yourself

Rule 2: Look after your colleague(s)

Rule 3: Look after the equipment.

Observe that Rule 1 is ALWAYS ‘Look After Yourself’. You are in the best position to do that. Don’t just ‘look’ but ‘see’. Don’t just ‘hear’ but ‘listen’. Don’t assume—THINK.

Rule 2 is not to look after your friends because often you will work with people you don’t like. One guy said to me, “You don’t like me very much, do you?”

I told him that he was wrong. I didn’t like him at all.

But he is still a colleague! One day you may need him to look after you.

Alarmingly, you will work with people who do not like you. No, really. No matter how likeable you think you are, somebody out there dislikes you with a passion.

Rule 3 means that you keep the equipment serviceable and safe. Repairs or replacements are costly and that can mean that there is no pay rise this year—clearly contravening Rule 1!!

Training

For the last forty years, almost, I have been primarily involved in training.

Some time ago there was a search to find a book from which to teach jet engines; the search failed emphatically. Every book that we uncovered was too deep. Most of them were to a level that assumed that the reader was intent on designing a new engine as opposed to the Licensed Aircraft Maintenance Engineer (LAME) who just wants to diagnose and repair.

Example: One book that was very large and thick had a page covered in italics; it turned out that this was an equation. After scanning it for a moment or two I realised that the equation could be reasonably simplified into one line, the need for constants and fluid densities did not really apply for practical purposes where only an illustration of the effect was required.

We were not training physicists or design engineers.

Ultimately I was advised that if a simpler book was require then I should write it myself.

This is what then happened.

But.

I insisted that the book would be written in the way that I like to teach and thus it was filled with cartoons.

This has had an upside and a downside.

There were publishers who railed against the use of cartoons; they said that there was no room for humour in a textbook. The other downside was that some people have said that they enjoyed the cartoons but they had no idea what the text was all about because they never read it!

The upside is that many Licensed Engineers, as well as Pilots, Technicians and Mechanics, have thanked me for writing it because they now understood the subject better because it was written in a light-hearted manner and kept the subject down to a simple form in simple English.

Let me explain to you what we are striving for in writing a textbook and carrying out training of any sort. Clearly, it is unlikely that we should be successful in achieving all the requirements listed but we should endeavour, during all training, to be able to cover most of these things:

Under the revised ‘Bloom’s Taxonomy’ we are looking at the following -

The new terms are defined as:

Remembering: Retrieving, recognizing, and recalling relevant knowledge from long-term memory.

Understanding: Constructing meaning from oral, written, and graphic messages through interpreting, exemplifying, classifying, summarizing, inferring, comparing, and explaining.

Applying: Carrying out or using a procedure through executing, or implementing.

Analyzing: Breaking material into constituent parts, determining how the parts relate to one another and to an overall structure or purpose through differentiating, organizing, and attributing.

Evaluating: Making judgments based on criteria and standards through checking and critiquing.

Creating: Putting elements together to form a coherent or functional whole; reorganizing elements into a new pattern or structure through generating, planning, or producing.

(from Anderson & Krathwohl, 2001, pp. 67-68)

Note that I said this was the intention for ‘all training’. So it is.

But.

At the end of the training session the onus is upon the trainee to implement all that they have been taught.

Something that is extremely disappointing is to teach a group of people the correct way to carry out a procedure—perhaps in accordance with the directive from an Aviation Authority or from ‘The Company’, and then see those same people, the very next day, continuing to use the wrong method because that is the Company ‘norm’, it is what they are accustomed to doing even if it is wrong or, even, hazardous.

This is something that occurs Worldwide. Often the trainer is battling against peer pressure, budgetary constraints, personnel deficiencies—in terms of numbers or aptitude, and people with static mindsets in positions that affect the workplace.

Peer pressure: “Don’t bother with that—this is how we always do it here.”

Budgetary constraints: “The Company cannot afford safety equipment—just do what you can with what we have.”

Personnel deficiencies: “We are short handed at the moment, you’ll just have to work an extra shift.”

Inflexible management: “Ignore the trainer—he’s an academic. Besides, he hasn’t been here long so he doesn’t know how we do things here.”

We trainers can only do so much. We can lead the trainee to knowledge but we cannot enforce implementation.

As you see, we trainers can write books that are simplified in order to help, we can put facts before the trainees, we can highlight hazards and give examples of where these things went very wrong for people but, finally, it is up to the trainees to put into practice what we have told them.

http://www.jetenginebooks.com/ 

"A Simple Guide to Understanding Jet Engines"

The postage rates for UK and US from Malaysia have gone up by 50%! Books are no longer classified as 'documents', they have become 'small packets'.

Last week it cost RM27 (£5.48) to send a copy of "A Simple Guide to Understanding Jet Engines to UK and RM38 (USD12.13) to send one to the US.

Now the cost has escalated to RM60 (£12.18 and USD19.15)

Given that 'Amazon' take a substantial lump of the cover price my publisher has gone from making a slim profit to a loss on each book overnight.

It is for this reason that sales of "ASGTUJE" is to be discontinued as a physical book on 'Amazon'.
It will only be available direct from the publisher at a reduced cover price but 'plus handling & postage'.

Please refer soon to:

http://www.jetenginebooks.com/

Please purchase "A Simple Guide to Understanding Jet Engines" direct from the publisher or, for Malaysia, from 'Kinokuniya' in KLCC, 'Mehraj' book sales in Kuala Lumpur or the bookshop in the departure hall of KLIA.

Overseas customers requiring a physical book will be asked to cover the cost of handling (post and packing).

Thank you for your kind consideration.

You Must be Choking!

Sorry about that.  Some things are just naturally irresistible!

The point of it is that I want to talk about ‘stall’ and ‘surge’.

Why?

Because there seems to be some confusion in the ranks. There have been questions posed that would lead me to believe that these are two aspects of a compressor that are not fully understood.

Firstly, are we talking about axial flow compressors or centrifugal flow compressors?

Both, really, but we will come to the centrifugal flow compressors later since they are somewhat different in their ‘cause and effect’.

Shall we take out an axial flow compressor blade and take a peek at it?

Hold it so that you are looking down from the tip to the root.

What do you see?

Yes, several things:

1.     It has an aerofoil shape, the same as a wing.

2.     It is ‘twisted’.

If we take out two blades and put them together, by holding the base of each blade firmly abutting (touching) each other, then we see something else.

That the gap between the blades, in the direction of airflow, is divergent – it gets bigger as the gas leaves it.

These designs in the blades are there to do one thing – to ‘do work’ on the air.

The turbine supplies energy to the compressor and the compressor uses that energy to bunch up the air.

Now we have to be very careful.

The flow of air through the compressor has to be (almost) uniform.

Not in terms of velocity but in terms of mass flow.

If we have 500 kgs per second going in the front of the compressor then we absolutely must have 500 kgs per second coming out of the back into the combustion section.

That is vital.

The velocity of the gas is, more or less, irrelevant and will depend on the rpm of the compressor and not (as many seem to believe) the speed of the aeroplane through the air.

Note that I have just suggested that the rpm of the engine is, for most engines, a variable.

Note that the cross-section of the blade is an aerofoil.

Aerofoils do well at an optimum angle of attack of four degrees (4°). This will only happen at one rpm.

That means that there is a compromise somewhere.

Listen to a jet engine starting up.  At some point in the start sequence you will, very likely, hear a rasping noise from deep within it.

This is a ‘stall’ occurring. It will always do this. You will never get a nice airflow over all the blades all the time to create that lovely angle of attack.

There are going to be times when the airflow through the engine does not match the speed of the blades (rpm). Start-up is one of those times. Every time.

If the angle of attack of the air on a blade is bad – naughty air! It may produce turbulence down the back of the blade.

Turbulence means that the blade is no longer ‘doing work’ on the air. But the turbine is still sending energy down the shaft to the compressor (remember that!).

It is unlikely that only one blade will stall.

It is more likely that a whole stage (row) of blades will stall. It may be the ones in the middle, the little ones at the back or, even, those hulking great big ones at the front.

If the conditions that created that breakdown of airflow over that stage are restored to normal, then the blades will continue to work.

If conditions do not return to normal there is a danger that other stages will also stall.

Why?

Because the stage that has stalled is doing no work on the air, which means that the air being received by the next stage is not at the best condition for it.

Similarly, the air leaving the stage in front of the stalled row is not being accepted by the stalled stage – slowing it down.

Air that changes speed is not at the same angle of attack that it was previously. This is why we cannot suddenly change the rpm of the engine because it will rapidly change the angle of attack on the blades.

We now have an engine that is in a state of stall.

The compressor is still receiving lots of energy to do the work with but it is doing less work. More stages stalling will reduce the workload even more.

How do we know that this stall is occurring?

Because the exhaust temperature will be going up, the engine is likely to be vibrating (because the gas is turbulent) and it is very likely that you will hear it.

What to do?

Close the throttle and watch the instruments. If the engine slows to idle rpm and the temperature comes down then run the engine for three minutes at cooling rpm (not necessarily idle – the RR Viper engine cools at a slightly higher rpm than ground idle), and shut it down to investigate the cause.

It may be that the temperature continues to climb (burning fuel with less load on the compressor and reduced air) and the rpm stays where it is.  Now all you can do is shut-off the fuel and hope that the bearings don’t suffer too much.

This last is what is called a ‘locked in’ stall.

But what if all the compressor stages stall?

Then the compressor is doing no work on the air at all. The high pressure air at the back can now come to the low pressure at the front of the compressor. It will do this suddenly and, almost, explosively.

You will hear a loud bang. If you are outside the aeroplane it will feel as if you have been punched all over by a giant fist. If you are very close to the engine it may knock you over.

If you are inside the aeroplane at the controls, you may see the exhaust temperature and rpm begin to rise. The rpm will only go up for a moment but the temperature will keep going up. This is a really good time to shut the fuel supply off. Of course, it may just be a ‘pop’ surge where engine ‘clears its throat’, as it were. Things may go back to normal immediately but it is still worth investigation.

Apart from discovering the source of the problem, what are we looking for after a surge?

Check the oil (SOAP) and MCD’s (Magnetic Chip Detectors) as well as the oil pressure filter and scavenge strainers in case the bearings have been damaged.

(The SOAP sample results will have to be compared with the previous SOAP results to see if there is a sharp up swing in the contaminant level.

NB: SOAP = Spectrometric Oil Analysis Programme. This is done by a lab unless you work for a very big major airline that has it’s own kit!)

Do a borescope check – especially on the rear stages where possible.

Check the turbine for ‘spatter’ – it will look like the sky at night with little ‘stars’ of melted metal all over the turbine blades and, often, the exhaust.

Naturally, look down the intake. Several times we needed to go no further than a quick peek past the first stage on co-axial (twin spool or dual-axial) engines.

So what about centrifugal compressors?  Do they stall? Yes. They do.

Try and stay with this because it gets a bit tricky.

Between the rotating part of a centrifugal compressor and the static part there is a gap.  Not a big gap but it is there.

The reason for the gap is that the air coming off the impeller vanes is quite thick, it has been compressed, it is hot and it is moving quite fast.

As each impeller vane on the rotating bit goes past a diffuser vane on the static bit there will be a ‘thud’ as a lump of compressed gas gets caught between the two. The air behind the impeller vane is not quite so ‘thick’ so the sudden increase in viscosity is really noticed by the diffuser vanes.

(Listen, if you get the opportunity, to a RR Derwent engine on, say, a Gloster Meteor going overhead at low level; it sounds like a V16 piston engine because of all the ‘thuds’ as each impeller vane’s air hits each of the diffuser vanes.)

The gap has to be wide enough – remember the gap? For the air to ‘spread out’ a bit before going into the diffuser to lessen this ‘thud’ because too much ‘thud’ creates too much drag – wasted energy. Too small a gap = too big in the ‘thud’ department.

But!

As the aeroplane goes up into the clouds, and beyond, the air gets thinner.

At some point the air will be so thin that, even with the impeller working very hard to compress it, it will slip around the gap. If air is going around in circles it will block off the air trying to get out of the impeller.

The compressor will now stall.

It is unlikely to surge (but it can happen) but the conditions of the stall are exactly the same as for an axial flow compressor.

So what causes a centrifugal compressor to stall?

Low air density - altitude.

There you have it.

Surge and stall made easy. I hope.

Now my brain has stalled, my temperature is going up and work is ceasing.  Time for bed after a quick refuel!

Heat

Before I write anything else about anything else, there needs to be a clearing up of confusion.

Just recently there have been a few misconceptions posted here and there. 

For instance, there is a person on ‘E News’ who has taken to using the expression ‘Ell-Beez’. This is usually in conjunction with the revelation that a certain celebrity (who is, invariably, completely unknown to me!) has gained, or lost, a few ‘Ell-Beez’.

Let us all, with one accord as distinguished Jet Engine Professionals, put these people into the light of knowledge.

The plural of ‘lb’, the accepted abbreviation for ‘pound weight’, is ‘lb’

It comes from the Latin ‘Libra’ meaning ‘pound’; the plural of this is ‘Librae’. Observe – no ‘s’.

Ergo, said ‘celebrity’ has gained, or lost, a few ‘Ell-Bee’. Not, perhaps, quite so catchy but much more accurate. It also avoids pitying looks from the intelligentsia who watch the show.

Now heat.

Heat and temperature are not the same thing.

Heat is a form of energy. We get ours from the Sun. Exclusively. Try very hard not to tell me that we can get heat from burning coal or wood. The energy that gave us both these fuels came from the Sun so they are ‘second-hand’ solar heat.

Cold is not energy. Cold is an absence of heat in the same way as there is no such thing as ‘dark’. Dark is an absence of light (which is another form of heat energy.

Temperature is a measurement of how much heat is present in any particular volume of… well… anything.

Let’s take an example.

10 lb of dry air at ISA (International Standard Atmosphere – 14.7 psi at 15°C) takes up the space of a sphere approximately 6.28’ in diameter.

If we pass this volume of air through the compressor of a jet engine, the compressor will make it smaller. We shall say that the compressor gives a CR (Compression Ratio) of 10:1.

Ten to one? Time for lunch – see you later.

Ah! Good food.

Where were we? Oh, yes. We are going to reduce the volume of air by a factor of ten.

It will now be 0.628’ in diameter or, if we convert that, 7.536”. Sit in the hand just nicely; just under an octave

Of course, you would not want it sitting in your hand because we have also compressed the heat in it by a factor of ten.

15°C now becomes 150°C – considerably more than the boiling point of water (at ISA).

It is exactly the same amount of HEAT but it is now occupying a smaller VOLUME of, in this case, AIR.

Of course, this is ignoring the work done on it to compress it. Since we are less than efficient, the work done to do the compressing will be mostly wasted in heat energy transferred into our bundle of gas and so the heat within our sphere will be much greater than it was at the start.

In other words, the temperature will be much higher. Much.

An axial flow compressor giving a CR of about 11:1 will give us an exit gas temperature of around 550°C. If you yearn to know how that feels then go to a friend who longs to kill him/herself with noxious gases. Ask them to light the cigarette and request that they suck long and hard on it.

When the tip glows brightly that will equate to around 550°C. Try to avoid the temptation to put your finger on it.

The HEAT in the cigarette end will be quite small but the TEMPERATURE will be very high.