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I mentioned earlier that thousands of airplanes take off every day with known faults. Somebody mentioned MEL (Minimum Equipment List) detailing what can be broken and still allow a plane to take off.

There are various documents involved and depending on the author / purpose etc it will come under different names. MMEL, MEL, DDG etc. Not sure, but these might also be Boeing specific terms. I won’t go into detail what the difference is between these as their purpose is in essence very similar.

They detail and define how many and what sort faults can be tolerated, what measures need to be taken to still take off.

Attached, as I thought it would be quite telling, the MMEL from Boeings 747-400 Dispatch Deviations Guide on Brakes. Have a look:




It will show the number of wheel brakes installed (16) and the number of wheel brakes required for dispatch (14). You can see in the remarks what needs to be taken into consideration and or done to allow so, For instance, there is a remark about take off and landing performance. It will be different with fewer brakes. So you might need a longer runway!

You will see there are No EICAS messages. Basically on the alarm panel in the cockpit nothing will show! But a placard needs to be shown in the cockpit as appropiate to remind the crew. Also, the crew will be briefed and it will be shown on the maintenance log of this aircraft prior to departure, so they can check and verify what they might have to do different.

So there you go: A fully loaded, Boeing 747-400 can take off with two of it’s Wheel brakes inoperable.

The Headline could be:

Or the headline could be

Both headlines are factually true and correct.

Which one do you think will make it into the news papers and onto social media??:Frustrati


Jeroen

It is appalling to see the way our media sensationalizes every single news. :deadhorse

Nobody (DGCA, Indigo or GoAir) has done anything wrong in this case. The faulty engines and frequent failures of specific batch of engines was analyzed and caught by EASA in its investigation. EASA issued a directive stating that A320 neo aircraft equipped with both engines from the faulty batch to be immediately grounded in Europe. DGCA followed the same instruction and three impacted aircraft were grounded. Rest 11 aircraft had only one faulty engine were allowed to operate under the redundancy that two engine aircraft can easily do a flight on one engine in case of emergencies.

After a point of time when DGCA felt that the single engine failures were also getting too frequent. They asked the rest 11 aircraft to also be grounded. EASA issued a statement that DGCA was being overcautious.

And it is not about profits for Indigo or GoAir, as they get compensation from P&W for non performance of engines. Please spare the thought that Indigo was putting passenger lives at risk.

Please note: Airtravel is the safest travel option in this world. And playing with safety is not an option. To check the validity of this statement, check when was the last air crash which was caused by equipment failure.

Something puzzling me:
The gearbox (at least its use in this case) is revolutionary. Everything else is evolutionary.
But the problems reported are not from the gearbox. What gives?

Regards
Sutripta

It does seem odd indeed. However, a lot of the problems are with seals and with areas in the combustion chamber, etc. As this engine is a sort of next-gen, ground-up design, those are the parts that are suffering. From my understanding, nearly every part has been redesigned or re-engineered to suit the new way in which this engine is functioning. If you have a chance to look at a GTF engine head on vs any older engine on the IndiGo fleet, you will see that it is possible to look through the GTF, there is a lot of open space that is to do with the high bypass ratio of the engine. In an effort to make this work, Pratt seems to be struggling.

The Pratt engine has a listed bypass ratio of 12.5:1 which means, by volume, 12.5 times more air is passing through without being burned. Clearly, they are trying something amazing and have been facing trouble as a result of not being completely market ready. Who knows if this means India will become a regular site for aircraft engine testing. We have it all here - cold, high altitude airports, heat, dust, heavy rain, hail - you name it.

To summarise - nearly every bit of this engine is new. Perhaps the fact that the gearbox is sealed is making it reliable. Gearboxes in other applications also tend to be quite reliable - in your own vehicle it is more likely for the engine to have a fault than the gearbox. Hope this helps.

A very intriguing discussion indeed. I have carefully gone through the last few pages and a couple of things continue to baffle me.

Someone mentioned that the tips of the fan in a turbofan usually exceed the speed of sound but apparently supersonic tip velocities are avoided in a turbo prop engine(TU-95 bear is an exception it seems). Why cant a turbo prop blade tip go supersonic?
What is the exact difference between a propeller and a fan. I have read that turbo props are most efficient at 325-375mph while turbo fans are efficient at 500-580 mph. Both setups have a turbine and compressor turning the rotating part that develops thrust, so what makes them efficient at different speeds? Is there a significant difference in the way they generate thrust?

In my view, new which is evolutionary should not cause problems for an established manufacturer. Even pushing the envelope is evolutionary, not revolutionary. So unless you are saying that the subsections/ modules giving problems is a revolutionary design, I'm still perplexed. (On the other hand, would also like to know why the said designs are revolutionary).

Add helicopter rotors, and ducted fans to the discussion.

On another note I wonder where GoAirs IPO plans stand now.

Regards
Sutripta

My question may be rudimentary and do correct me if I am wrong.

A few months back, I heard that Indigo (most affected Indian airline due to a320neo) used to fly with only one engine to save fuel. Is it technically possible to fly on one engine throughout the flight? Is this one of the attributes for its engine failures?

I read at someplace that was only for Taxi-ing and that too when it met certain criteria- over 10 minutes (and one had to ensure the second engine still got enough warm up time), weather, etc. I may be wrong though

No, they absolutely don't fly on one engine. Only in an emergency as the plane is capable of flying on one engine. But they would never do it on one engine on purpose.

Twin engine plane do taxi on one engine to save fuel though. Some carriers have specific rules for it. Sometimes it can be a bit tricky as you have to compensate for the asymmetric thrust. If you are running the right engine and have to take a very steep right hand turn, you might run into problems. Takes a bit of time to light the other engine. Also four engine plane sometimes shut down engines during taxi to save fuel.

Jeroen

Technically very much possible but to save fuel, never. With one engine, the fuel consumption would be pretty high and the overall range would also take a hit!(experts please correct me if i am wrong). Plus with strict airline rules, i don't think that any airline would do this. This news that you heard is definitely wrong.

Sounds like a typical WhatsApp hoax and a vicious rumour. But I'll let the experts reply :-)

Thank you for asking the question. Though it may sound rudimentary to some it is something that at least some flyers would worry about. And an answer could help allay the doubts of some.

Three parts to the answer.

Part One of the answer - in modern airliners it is perfectly possible to fly on one engine alone as the thrust to weight ratios are now so good. In fact the A320 or the B737 that one typically fly these days could climb out on a single engine even with a full load. Though one engine blasting thrust and the other shut down and creating drag will lead to an assymetrical situation on at least 2 axis and need some healthy pilot control to compensate for it. All twin engine jet airliners and large twin engine turboprops you are likely to fly today are certified and thoroughly tested for single engine ops. Very small twin engine propeller driven planes may not be able to maintain stable flight on one engine.

Part Two of the answer - Flying on one engine will not save fuel compared to flying on both at cruise settings. The idle engine will add to the drag and asymmetry. A minimum power setting is commonly used when descending down to land. They idle both engines and gravity helps the aircraft glide down the last 150 to 220 kms thus saving fuel. After landing some airlines practice single engine taxing - that does save a tiny amount of fuel. But with scale the savings could be large enough to count. this practice may be the source of the rumour.

Part Three of the answer - no airline that I know of ever flies with one engine on a two engine airliner as a policy or to allegedly save fuel. In my career in this field my team has intimately dealt with well over 120 airlines on technical matters and never ever seen or heard this - don't ask more on my work as this is not the place for details but this is my own professional experience and not internet buzz. Even if some budget penny pincher head office guy came up with this policy no sane pilot will agree to it. His or her personal license could be at stake. If you fly on a single engine, for whatever reason, it must find its way to the log book and to the regulators desk.

To answer an associated question if you permit i.e. what happens if both engines fail. Well other than praying hard the aircraft can be glided down in a ratio of ~1:10 of vertical descent: forward flight. It can vary by 25% plus or minus because of weight, weather etc. So if you are at 36,000' or ~11 kms up you have a theoretical 110 kms of forward flight to figure out a place to land. Of course easier said than done and a moment of deep stress for the crew but it is a real safety buffer and has been used in real life a few times. 110 kms may sound a lot but it translates to only a few minutes of flying time.

I hope this helps. Share it with others as our industry suffers more than its fair share of rumour mongers and yellow journalism.

To add: it depends a bit on the weight but in most cases with one less engine the aircraft in question won't be able to fly at its most optimum altitude. Any lower altitude and you incur a stiff fuel penalty. It's more relevant for twins on long haul as their fuel planning relies heavily on being able to fly at the most optimum altitude. During the flight as they burn of fuel, the aircraft becomes lighter and they will climb a little higher. In theory you can calculate a continuous optimum ascend. But ATC won't allow it so usually you climb in steps of 2-4000 feet at the time. With one less engine be it on a twin or a four engine plane you won't be able to maintain the most optimal altitude and you will need to drift down to a lower altitude. Jet engines are less efficient at lower altitudes and you have the additional drag to content with. With thrust coming from one engine only, you will need to dial in opposite rudder and sometimes use ailerons as well. Causes a lot of drag.

Getting a twin rating is just spending quite some hours going through all the usual manoeuvres with one less engine and having that engine cut out on you at awkward moments.

Jeroen

That reminds me of the 767 which suffered from dual engine failure and then landed on an abandoned runway. It was one real lucky set of people up in that flight. And the skills of the Pilot, especially one of them(I am not sure who) who was trained well in flying gliders who was able to use similar skills to land the plane in one shot, since there is no second chance.

What worries me are if Indian pilots are equally trained and competent. I am not judging that they are not, but wonder if there are similar incidents at least on a simulator to train for situations where there could be dual engine failure.

Another aspect in our country is the availability of airports/runways for such an emergency. In and around Bangalore, I can think of five runways. KIAL, HAL airport, Yelahanka airbase, Kolar Airstrip and Hosur airstrip. However, as we move to the rural belts, I am not sure if we have enough number of airstrips. Of course such emergencies are really rare, if they actually happen. But the preparedness is something that should always exist.

How long can an A320 manage with one engine? I am thinking of an event of a single engine failure after taking off from Port Blair. Can the aircraft continue to Chennai(1.5Hr flying time usually) or should it turn back to Port Blair? Can any person from this industry comment?

Dear audioholic, thank you for your questions some of which are surely on the minds of many flying passengers. Let me try and answer as best as I can.

This was the famous incident of the Gimli glider. The pilot in question Capt Robert Pearson still alive and well in his eighties.
Three parts to the response:

Part I: Bad practices with the regulator and the half baked training schools has left a lot to be desired. Some institutes such as IGRUA do a thorough job some others less so. However in fairness to the airlines there is a difference between a person 'passing out' with an incomplete training and an airline actually recruiting him. As an example if he has 100 hours of real flying and 300 hours on his log book it will require only some time on a simulator or in an interview (with an experienced interviewer) to find this out. Also Indian carriers are not necessarily recruiting from second grade training centres. Many Indian pilot aspirants for this reason go to USA to get their training at considerable cost. The Govt is moving to digital log books hooked to the aircrafts' systems. It will hopefully put an end to this tragic practice. Sadly, a reflection of a wider national malady, no one has been convicted for this criminal practice.

Part II: Yes pilots of Indian carriers undergo periodic training on simulators for emergency situations. Whether it specifically covers all engine failure would vary with airline but single engine ops, cabin fire are always trained for. Helicopter pilots always train for an all engine out landing by auto rotation and how to avoid the black zone known as the dead man's curve. Landing a chopper without power is more difficult by a degree due to the limited forward motion of the machine.

Part III: Thanks to the PW1100G engine we have just seen an unusual number of inflight engine shut downs and an equal number of successful and safe landings on the functioning engine. All those were Indian pilots on Indian carriers.:thumbs up

Since 1980 ie 38 years ago there have been 18 known cases of all engines failed across the world. Compare it with the ~36 to 40 million flights per year in recent years. This is only for airliners and data from China and some parts of Africa is incomplete. The chance that our home will be hit by an earthquake is far higher. Insurance company actuarial tables place the risk of an Indian dying in an earthquake at between 1:30,000 to 1:10,00,000.

India has about 350 air strips - civilian, airforce, private, emergency and abandoned WW2 ones. In Udaan III which is being rolled out the Govt plans to activate all of them to provide regional air transport to most district head quarter towns.
6 hours is the certified time on one engine for an A320. If there is an engine failure close to the start of a flight the Capt would usually opt to return, shed fuel and land. If he were closer to Chennai he/she would in all likelihood continue to head to Chennai.