[alpha1]

I am sure many of you would be aware about the issues being faced in the Airbus A320 Neo aircrafts having P&W turbofan engines.

DGCA has grounded the planes till the problems are resolved.
The same problem(s) has/have been observed elsewhere across the globe.

Folks from the aviation industry background - can you guys inform about the specifics of the issue? All it says is that the engines were stopping mid-flight in the air.

https://www.marketwatch.com/story/ai...lem-2018-02-09

[Raj_RD]

Well, the problem is with the knife edge seal in the high pressure compressor aft hub of the Pratt and Whitney 1100g engine which is causing the in-flight engine failure. While the neo's of Spirit Airlines had freezing problems which resulted in flying around 30,000ft, but this has a big effect on the fuel efficiency of the aircraft. Airbus is not at fault here. Hope P&W will fix this asap.

[Jeroen]

Couple of thoughts and comments. The problems with the seal are the latest issue, but this particular engine has been plagued from various issues during its short life span. Initial deliveries of this engine were ramped down significantly as there were faults with the titanium fan blades. Apperently there have been several other issues as well, that until recently were all rectified. I have yet to find a comprehensive technical overview of all the problems so far. The problem with the seal being the most recent one. It lead to grounding of the affected airplanes in Europe and India.

On the various aviation forums I hang out, I see a lot of refences made to how P&W is being run as a company and where it differs from the likes such as GE and RR.

They have betted heavily on this new engine and are winding down most of their other products. So it is a all or nothing scenario it seems. They have little to fall back on financially.

Apparently, it is also their first completely inhouse designed engine for several decades. So they have to go through a very steep learning curve to get such a brand new engine, incorporating a lot of new design and technology, to the market quickly. Last year they had quite some troubles ramping up their supply chain as well.

These sort of problems with engines, usually means the engine has to be taken off the plane, brought to a specialized workshop and be modified. Although taken an engine of an airplane is a fairly standard and routine operation it is still complex and routine and obviously you will need sufficient spare modified engines to swap them around and get the fleet back into the air.

Jeroen

[Turbanator]

Originally Posted by Jeroen

These sort of problems with engines, usually means the engine has to be taken off the plane, brought to a specialized workshop and be modified. Although taken an engine of an airplane is a fairly standard and routine operation it is still complex and routine and obviously you will need sufficient spare modified engines to swap them around and get the fleet back into the air.
Jeroen

Thanks for the insights, One noob question, can the Aircrafts equipped with P&W fitted with engines from other manufacturers like GE / RR without much changes or is it too complicated?

[AkMar]

Originally Posted by Turbanator

Thanks for the insights, One noob question, can the Aircrafts equipped with P&W fitted with engines from other manufacturers like GE / RR without much changes or is it too complicated?

I don’t think it would be that simple. The pylon or mounting of the engine on wing will have to be changed. Software changes too could be required. Experts can explain better.

I don’t think it would be a commercially viable exercise for any airline, as they already operate on thin margins. Better choice would be to ground the aircrafts and accept compensation offered by manufacturers which is not a small amount

[torquecurve]

The larger issue here could also be the economics of the whole thing for Airbus. The 320 is in a fiercely competitive space as it is, with a large order book notwithstanding an issue like this can dent confidence and lead to cancellations. Case-in-point being the Tristar (Lockheed L1011) debacle which was mainly due to first the delay in the Rolls Royce made engines which for its time was an advanced design (3 spool vs 2 spool and Carbon Fibre blades IIRC), however was untested.
With IndiGo being a large operator of the type, grounding of these aircraft will affect schedules. The ETOPS rating for these aircraft (with two PW) engines has been effectvely withdrawn meaning they are limited to over land flights only.

http://avherald.com/h?article=4b4c4509
Old But relevant news

[URL = "https://www.cnbc.com/2016/07/11/qatar-airways-considering-boeing-737-max-after-cancelling-airbus-a320neo-order-ceo.html

Though Qatar airways finally went with the A321 NEO, I am sure the negotiations must have been to Airbus disadvantage.

If I am not mistaken IndiGo was betting heavily on the A320 (200 plus orders). This grounding and delays could be detrimental to the airline and other LCC (Low Cost Carriers), which for cost reasons operate a single type (or family)

[V.Narayan]

First the good news, if you can call it so, is that a single engine failure can be managed successfully as the fine pilots of Indigo and Go-Air have been forced to demonstrate several times lately. But you don't want to make a habit of it. The bad news is that so many mid-air engine failures in quick succession is almost unheard of. On an average a mid-air engine failure or involuntary shut down happens once in 1.6 million flights a year globally or 22 to 25 incidents a year. So from a statistical point of view what we see happening is whacky! Pratt & Whitney have supplied 113 such PW1100G engines of which 45 are currently in India on Airbus A320 neo planes. Here 'neo' stands for new engine options.

These engines have been giving trouble even after a delayed and difficult entry into service. Reports say there have been 69 instances, in India, in 2 years where the airlines changed engines overnight when routine daily inspections revealed all was not well. At periodic intervals or when caution demands it an engine is checked visually with a magnifying boroscope. Certain parts especially the blades, the seals, the point at which the blade tip (almost)brushes against the inner cowling ring etc are visually checked with a magnifying boroscope inch by inch. In these checks, in India, unexplained & unexpected oil leaks were surfacing which led to feedback to P&W and the engine changes. I do not know what has been surfacing in Europe on the daily/weekly checks.


Magnified about 15X this is the kind of damage you search for. This is a very obvious one. Some like seals or bi-metal strips peeling off can be discreet and need a senior engineers skill to spot.

As of now I wont guess why these engines have needed so many changes or why they auto-switched off in mid-air. Let the investigations be completed. The press reports are there to read and some have inserted 'technical' sounding sentences which may or may not be relevant. What has been disclosed by P&W is that metal dust is finding its way into the engine oil which leads to the sensors shutting down the engine as a precaution against fire. Others have reported fuel lines getting choked. Either way it is very serious.

Why these engines? The PW1100G is a geared turbofan. It is the third generation (or fourth as some insist) of jet engines. The chart below shows graphically the three stages of jet engine evolution in the last 75 years.

Courtesy Economist.com

In a turbofan, as most of you know, energy is extracted out of the hot fast flowing gases at the rear and used to run (1) a large slow efficient fan in the front that aids fuel efficiency; and (2) a compressor. The PW1100G has a bypass ratio of over 12:1 ie for every one unit of energy flowing out hot and fast 12 units flow out cold and slow which is way more efficient. It is claimed to give a 16% better F.E. than non-geared turbofans. A typical modern non-geared turbofan would have a bypass ratio of 7:1 to 10:1. Think of it as 'gearing down' the airflow. If you have a heavy airliner flying at Mach 0.8 you want engines that push out a large mass of air at roughly the same speed and not a tiny mass blasting back at a much higher speed.

The challenge over the last 40 years has been that you want the frontal big fan to run at ~2000RPM* and the compressor behind at ~5000 - 6000RPM* even though both for many reasons run on the same shaft except in some Rolls Royce engines. The RPM is limited by the speed of the tips of the blades of the big fan. The tip speeds reach ~1.5X the speed of sound in the turning axis and as the aircraft is flying forward relative to still air in three dimensions their velocity is usually ~2.5X the speed of sound. That supersonic sound of the blade tip is the loud electric saw wheeee you hear as the engine climbs the aircraft after takeoff.

In a PW1100G geared turbofan a gearbox weighing ~110 kilos is fitted just aft of the big fan which enables fan and compressor to each turn at its optimum RPM. Pratt & Whitney designers have been working on this since 1988. The trick is in how do you design a gearbox that is a cube with each side of ~0.5 metres in size to absorb and distribute the equivalent of ~ 40,000 shp.

As of now a new generation engine is facing unprecedented trouble and it will require a lot of testing to restore the regulators confidence.

* these are only indicative numbers to explain the concept. Each engine will have its own RPM plus or minus 15%

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To Turbanators question which I just saw - you can have a worldwide programme of mating a new engine to an existing airframe and it has been done a few times with great success in the civil world. The military do it more often. Challenge will be in the pylons, plumbing, electrics, software and some redesign of the cockpit. Also have to look at aerodynamics. You'll be surprised how mofications measured in centimeters can have a completely out of proportion impact to aerodynamics, turning, stability etc. Usually the airframe OEM and engine OEM would work together on what will be a significant 12 to 24 month long programme. It cannot be done at the airline level.

[Jeroen]

Originally Posted by Turbanator

Thanks for the insights, One noob question, can the Aircrafts equipped with P&W fitted with engines from other manufacturers like GE / RR without much changes or is it too complicated?

I would think it would be very complex and expensive. It requires quite some mechanical and electronics adjustments not just software, but the actual instrumentation, control boxes etc. I'm also quite sure the certification will need to be redone (partly) as well. Different engines give a different performance and all of that would have to be tested, verified and certified. Lengthy and costly process.

There have been jets designed in the past that were equipped with engines from different manufacturers. So on a 747 you might find P&W, GE, RR, but as far I'm aware they are not interchanceable. It's often the carriers who has the last say on what kind of engines go on the plane. Partly to do with their own preference, fleet and maintenance standardisation etc.

Jeroen

[srishiva]

I read about these engine failures aboard a Indigo flight to Chennai. There was a magazine in which the article was talking about the single engine failures. The author had also written that its being made out more than what it is since both engines have never failed :( I think India has been slow in taking these out of business than the rest of the world.

[Raj_RD]

The Neo's of Air India are fitted with the CFM Leap 1A engines. But GoAir and IndiGo chose the P&W engine. The CFM engine also had some problems but they are solved now i guess.

[V.Narayan]

Originally Posted by srishiva

I read about these engine failures aboard a Indigo flight to Chennai. There was a magazine in which the article was talking about the single engine failures. The author had also written that its being made out more than what it is since both engines have never failed :(

Sadly we are a country full of over informed journalists. I don't see P&W resolving this anytime soon.

I think India has been slow in taking these out of business than the rest of the world.

Not quite true but yet partly so. Each regulator has to take a call based on what's happening in its area and with its operators and what is the situation on the ground. EASA banned flights by all aircraft with both engines in the affected category about 3 to 4 weeks back but permitted flights overland where one engine was of the unaffected batch. DGCA was in a wait and watch mode as such decisions taken too early also create disruption and protests from the very same passengers who may now say why not earlier. EASA is the gold standard in the aviation industry worldwide. Even the FAA is a step behind in process and independence. Partly due to being independent of a single country EASA is truly independent and impartial. I wont express my views on our DGCA lest I am banned from Team BHP.

[2000rpm]

I am very happy with the decision to ground these planes. I take 2 flights atleast every week and Indigo frequency is so high that travelling by Indigo becomes unavoidable. I was absolutely unhappy when earlier the ministry decided not to ground the plane.

The ministry has finally woken up and has done the right thing. This was a disaster waiting to happen.

[Jeroen]

Originally Posted by srishiva

The author had also written that its being made out more than what it is since both engines have never failed .

It is true that there have been very few dual engine failures on Jets for the last couple of decades. Jet engines are typically extremely reliable. It is one of the reason that we see twin engine planes on long haul routes as well.

Twin commercial jets are operating under the so called ETOPS regime.
See https://en.wikipedia.org/wiki/ETOPS

Simply put it details how far a twin engine jet can be from the nearest suitable airfield. Over the last decades it has been significantly increased and thats how we see twin jets on what previously was 4 engine exclusive.

An engine failure on a twin Jet is a non event in the sense that as they operate under ETOPS they will always be able to reach a suitable alternate. They can fly, with some limitations on one engine. So as a passenger you might not even notice to much about it.

But no misstake, loosing an engine anywhere during the flight, especially on a twin is a real emergency for no other reason that if the other one fails you are going down. No matter what. Pilots when faced with problems follow a very strict regime. That means that when something break after ensuring safe flight the next thing is they will figure out what if the next one breaks. With only one engine left, there are no options and you must land at the nearest suitable airport.

The fact that we have seen so many issues with this particular P&W engine is a big thing too in my opinion. Because nothing like this has happened before and it might affect the ETOPS ruling for planes with these engines. So, it is very rare these days and the impact is far reaching.

Just because nobody has died, doesnt mean its a big thing!

Jeroen

[Turbanator]

Originally Posted by V.Narayan

Sadly we are a country full of over informed journalists. I don't see P&W resolving this anytime soon.

He may have lifted from here-

European Aviation Safety Agency (EASA) has said the Indian decision is a "unilateral" one with which EASA wasn't involved, adding that a complete grounding "is not deemed necessary for the time being."

http://avherald.com/h?article=4b5fedf4&opt=0

As a layman, many times I get little paranoid if both pilots are young especially in low-cost airlines in India, am not aware if the training and prerequisites of flying an Airbus here and in Europe are same or different or even within Indian if there are any differences in experience or training within airlines. If this is indeed correct, then Indian authorities have played safer correctly.

[A350XWB]

Originally Posted by torquecurve

The larger issue here could also be the economics of the whole thing for Airbus. The 320 is in a fiercely competitive space as it is, with a large order book notwithstanding an issue like this can dent confidence and lead to cancellations.

Or, they can switch the engine choice to CFM LEAP 1A. Airbus has stopped accepting the engines/shipping aircraft with PW1100G (news). Qatar CEO slams PW for the delays (news) & (article)

Originally Posted by Jeroen

I would think it would be very complex and expensive.

As far as I know, the B787 has a standard electrical interface to allow an aircraft to be fitted with either Rolls-Royce Trent 1000 or GE GEnx engines. The engine change was intended to take 24 hours. But I don't know whether anybody in the industry is actually utilizing/going to utilize this feature, due to a lot of other factors.