Plain Aviation

the life of a planespotter and true avgeek

Tag: engine

Singapore Airlines 777 Engine Fire?

Early in the morning of Monday June 27, a Singapore Airlines Boeing 777-300ER (registration 9V-SWB, 9 years old) operating flight SQ368 from Singapore Changi International Airport (SIN) to Milan-Malpensa International Airport (MXP) suffered an engine fire after an emergency landing back at Singapore that was warranted by an engine oil warning that the crew received shortly after takeoff.

Extent of damage to the right wing – Photo from Channel New Asia

The aircraft departed from Changi Airport at 2:05am local time and was climbing out when the cockpit crew received an engine oil warning message. As a result, they decided to divert back to Singapore as the airplane was deemed unfit to fly to Milan. The aircraft made an emergency landing at Singapore at around 6:50am, during which sparks were observed and the starboard (number 2) engine caught fire. The aircraft came to a stop on the runway and the fire continued to burn through the engine and the wing as passengers remained in the aircraft. The airport’s fire crew arrived at the aircraft 2-3 minutes later and put out the fire within a couple of minutes. Passengers then deplaned from the undamaged port side of the aircraft via mobile stairs. None of the 222 passengers and 19 crew were hurt in the ordeal. Singapore Airlines has offered alternative flights to Milan and accommodation in Singapore for all affected passengers.

Passengers disembarking via mobile stairs – Photo from Channel News Asia


Though an engine fire on a sophisticated aircraft like the Boeing 777 is already a significant event, what makes this incident even more worthy of attention is the fact that it comes less than a year after the British Airways 777 engine fire at Las Vegas McCarran International Airport in September 2015 that resulted in 14 injuries. The aircraft involved in that incident was a Boeing 777-200ER (registration G-VIIO, 17 years old) with 157 passengers and 13 crew operating flight BA2276 from Las Vegas McCarran (LAS) to London Gatwick (LGW). What happened was that the aircraft suffered an engine fire during the takeoff roll at McCarran International, causing the crew to abort the takeoff and call for an emergency evacuation.

Both of these aircraft were Boeing 777’s, and both also happened to be equipped  with General Electric GE90 engines, though the Singapore Airlines plane was a 777-300ER with GE90-115B’s and the British Airways plane was a 777-200ER with GE90-85B’s. The similarity of engine and aircraft types have caused people to speculate whether or not there’s an issue with the GE90 engines that’s causing the repeated incidents.

Source: discussion:

British Airways fire:



Are airplanes getting smaller?

After decades of evolution in aircraft technology that have led the aviation industry from the Wright brothers’ first prototype aircraft to the Airbus A380, it’s hard to imagine that in recent years aircraft have actually been shrinking in size. Orders for the Airbus  A380 have been recently been dwindling; Boeing cut production of the 747-8 to only 6 frames per year; and the Boeing 747-400 is currently in the Continue reading

What is a trijet in airliner terms?

A private Boeing 727 trijet. Photo by Andrew W. Sieber CC 2.0

As you can probably tell already, the term trijet refers to any commercial jetliner with three engines. Normally they either have all three engines mounted aft of the cabin and near the tail as seen on the Boeing 727, or two mounted on the wings and the third mounted at the tail as seen on the McDonnell Douglas MD-11. One common feature of all trijets is that their third engine is always going to be embedded inside the vertical stabilizer to ensure symmetrical thrust output. While this feature increases the difficulty of design, production, and maintenance, the cost-savings of operating trijets over four-engined airliners is definitely worth it.

Origins of trijets

Trijets were originally intended to be a cheaper alternative to four-engined jetliners in the 1960’s to 1980’s when restrictions were in place against twinjets due to concerns over reliability and redundancy. Trijets are much more cost-effective than their four-engined counterparts such as the Douglas DC-8 and more recently the Airbus A340 as their lack of a fourth engine decreases production and maintenance costs while saving fuel. These benefits were very attractive to airlines in a time of rapid growth in the industry and led to a “trijet craze” in the 80’s.

Design of the third engine

Just like boats moving in the water, aircraft need to have their engines thrust that is symmetrical on both sides in order to fly straight. Designs for twinjets and four-engined airliners are straightforward because they simply mount half of the engines on the left side and the other half on the right side to create symmetrical thrust. But with trijets, the only place that the third engine can be mounted is at the very center of the aircraft. As it would be impossible and extremely impractical to mount the engine anywhere on the fuselage, the only option left is to embed it into the vertical stabilizer. But with this design, engineers must also consider how to deal with the hot exhaust gas from the engine that could potentially cause structural damage. On the Lockheed Tristar and Boeing 727, engineers have designed an S-duct that runs through the vertical stabilizer and channels hot exhaust gasses from the engine to the very rear of the aircraft, where the APU exhaust would be.

Rear-view of a Lockheed Tristar showing the S-duct of the third engine. Photo by Alan Wilson CC 2.0

On the Douglas DC-10 and McDonnell Douglas MD-11 however, third engine simply runs straight through the vertical stabilizer with its intake and exhaust at the front and rear of the stabilizer. This configuration is known as a “straight” layout, and while it may reduce design complexity and simplify maintenance, it is less aerodynamic than an S-duct.

A KLM MD-11 with the distinctive “straight” layout. Photo by Maarten Visser CC 2.0

Decline of the trijet

The quickly dwindling numbers of trijets around the world can be attributed to the rise in popularity of twinjets. Trijets made their debut and peaked in popularity in an era when the FAA did not allow twinjets to fly on a route that would take it farther than 60 minutes worth of flying time away from any airport en-route. This regulation was known as the 60-minute rule, and essentially meant that twinjets were not permitted to fly long-haul routes over oceans or uninhabited terrain. The same restrictions did not apply to trijets, and therefore they were able to enjoy similar certifications compared to four-engined airliners while remaining more fuel efficient. But in the 1990’s, restrictions against twinjets laxed as technology improved. Twinjets were allowed to fly more remote and direct routes as long as they had the proper ETOPS certifications. As a result of this, the role and status of the trijet shifted from what was a cheaper alternative four-engined jet to a more expensive version of a twinjet; essentially these reduced restrictions stripped away the only real advantage that trijets had over twinjets. With the introduction of increasingly reliable and powerful engines such as the General Electric GE-90 and Rolls Royce Trent 1000, there is no longer a need for a third engine onboard traditional airliners that would only increase fuel burn and maintenance costs.

We can agree that trijets have an aesthetic appeal that cannot be found on any other type of airliner. While there are still several trijets in service with cargo airlines and minor carriers, their numbers are quickly declining. While I don’t think aircraft manufacturers are going to redesign an aircraft with three engines, I sure hope that I’m wrong.



Pros and Cons of planes with rear-mounted engines

A Delta Connection Bombardier CRJ-900 with two rear-mounted engines. Photo by Andrew Cohen CC 2.0

Ever noticed that some airliners have a sleek-looking T-tail and engines mounted at the rear? This design is found most commonly on smaller aircraft such as regional and private jets. Some people hate it, while others think it looks sleek and stylish. Now you may be wondering why some aircraft have engines at the back and others don’t. There are actually several reasons why aircraft manufacturers would place engines at the rear on aircraft like the Boeing 717, 727, McDonnell Douglas MD-80, and Bombardier CRJ series to name a few.

Under-wing clearance

Agreeably the main reason why an aircraft would have its engines mounted at the rear is because there isn’t enough clearance underneath the wing to mount the engines without having to install massive landing gear. Take a look at the image of the Bombardier CRJ-900, and notice how little space there is underneath the main wings. This would explain why rear-mounted engines are common only on smaller aircraft. If you were to install the engines underneath the wings, chances are they would be able to touch the ground, which is for obvious reasons completely unacceptable. Therefore, the only sensible location for the engines would be at the back of the fuselage.

Noise considerations

An obvious benefit of rear-mounted engines is the reduction in engine noise, which is disturbing to and disliked by passengers. Moving the engines back to the rear and away from the main cabin would reduce the amount of noise making its way into the cabin and increase passenger comfort. While this wouldn’t necessarily be the primary reason to have rear-mounted engines, it is definitely a consideration.

Lower risk of damage

The engines are always the most expensive part of an airliner, and therefore airlines want to keep them safe to prevent costly maintenance bills. Wing-mounted engines are more likely to suffer damage than aft-mounted engines, as they are closer to the ground and can collide with ground objects or suffer scrapes during landing. Aft-mounted engines are farther from the ground and somewhat shielded by the wing and fuselage.

Cons of rear-mounted engines

Every pro has a con that comes with it, and thus aft-mounted engines also have their drawbacks. In case you haven’t noticed, all aircraft with engines at the back also have T-tails. This is because there wouldn’t be enough space for a standard vertical stabilizer if the engines are also at the back. The issue with T-tails is that they can potentially enter something called a deep stall, which is a type of stall that pilots cannot recover from.

Illustration of a deep stall by Wikimedia user GRAHAMUK CC 3.0

A deep stall typically occurs when the aircraft pitches up at too high an angle of attack. During a deep stall, airflow to the tail-mounted stabilizer is disrupted by the main wing, rendering the elevators useless and disabling pitch control. This phenomenon led to the crash of British European Airways Flight 548, which was operated by an aircraft with a T-tail. Scary as it may sound, a deep stall isn’t as big of an issue as you may think, and aircraft manufacturers make it so that it is extremely hard to enter one, but nevertheless possible.

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What’s that barking noise you hear on the A320?

If you’re an aviation enthusiast like the rest of us or you regularly pay attention to what’s happening during your flight, you may have noticed that the Airbus A320 produces a very audible “barking noise” while on the ground. Most of the time it’s heard prior to or during taxi departing from the airport. Those of you who have noticed it can probably agree with me in that it’s a very distinct noise, most similar to a dog barking but much more mechanical, like a motor failing to start. The noise comes from something called the power transfer unit, or PTU for short. What the PTU does is that it transfers power (hence the name) between the different hydraulic systems so that each individual system has an appropriate amount of pressure. What people normally find strange is that this PTU noise only heard on A320 aircraft, never on the Boeing 737 or Airbus A340. This is because the A320 has a unique hydraulic system that isn’t found elsewhere. The exact technical details of the A320’s hydraulics system is definitely beyond my knowledge and probably beyond your interest, but the A320 has three different hydraulics systems whereas the Boeing 737 only has two, and therefore the A320 needs to transfer pressure between its three systems more frequently than other aircraft and therefore it requires a more powerful PTU. And typically with heavy machinery the more powerful it is the noisier it will be, which is why the PTU on the A320 is audible from inside the cabin. The PTU activates mainly after Engine 2 (starboard) has been started, and since the A320 somtimes taxi’s on one engine to save fuel, the PTU can also be heard during taxi prior to approaching the runway when pilots would start the remaining engine in preparation for takeoff. Next time you’re flying on an A320, be sure to look out for the sound of PTU if you haven’t already, it’s definitely hard to miss and very cool once you know what you’re listening to.

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My thoughts on the Airbus A340 family

To be blatantly honest I’m quite fond of the A340 as it’s the only four-engined single decker aircraft that is in widespread use, unlike the Ilyushin Il-96, which is currently operated for passenger service only by Cubana. Despite being an Airbus aircraft, the A340 has a surprising amount of character. I’ll probably receive criticism for this but to me it just seems as though Airbus planes are more down-to-business and have less finesse and stylishness than Boeing aircraft. The A340, like the A330, does feel somewhat lacking in elegance, but it makes up with its unique as a four-engined single deck aircraft. The A340 comes in four different variants: -200, -300, -500, and -600. As any plane spotter worth his salt should know, each variant is aesthetically very different from the others, especially when it comes down to proportions.


The oldest and shortest A340, the -200 is visually quite interesting, not 100% in the best way. Like the 767-200, its fuselage is a bit too short for its height and wingspan (which is longer than its fuselage), making it look rather stubby and quite awkward. It’s powered by the CFM-56 engines which produce between 139-151kN of thrust and look appropriately sized on the -200, maybe somewhat on the small side. It was unpopular with airlines due to its awkwardness, and therefore only 28 were produced.


The A340-300 was launched together with the -200, and has a longer fuselage in exchange for slightly reduced range. The fuselage length and general frame proportions of the -300 are much better than the -200. However, the two variants use the same CFM-56 engines, despite the -300 being considerably larger. Therefore, the 4 CFM-56’s on the -300 appear way too small for such a large aircraft, and again are quite awkward. Engine sizes aside, the A340-300 is a well-designed aircraft, evident in its popularity among airlines.


An improved version of the A340-300 and designed to be the world’s longest-range commercial jetliner, the A340-500 features a stretched fuselage and significantly larger and more powerful Rolls Royce Trent 500 engines to compensate for the size increase. The Trent 500’s are an absolute marvel second only to the GE-90, and the ones fitted on the A340-500 are able to produce up to 260kN of thrust. These massive engines combined with the -500’s perfect frame proportions make it without a doubt my favorite A340 variant.


The largest and most impressive A340 variant, the -600 was designed the compete with the 747. It features an even longer fuselage and slightly souped-up Trent 500’s capable of up to 275kN of thrust. I can understand Airbus’ need at the time for an aircraft capable of competing with the 747, and they’ve serious outdone themselves with the A340-600. At 75.36 meters long, it’s longer than both the 747-400 and the A380 but marginally beaten by the 747-8. As a single-deck aircraft, the A340-600 is perhaps a tad bit too long to be aesthetically pleasing, which is why I favor the -500.


The A340 is interesting as a family of aircraft in that its variants are aesthetically very different, much more than what you would find between variants of say the A330 or 777. Pouring over these details that regular flyers wouldn’t even notice is what keeps us plane spotters awake at night but nonetheless entertained.


Iran Air orders 118 new Airbus aircraft

Iran Air was founded back in the 1940’s, and in the 70’s and 80’s it was a leading airline of the world, comparable to Emirates today. Sadly, as a result of the Iranian Revolution and unrest in the region, Iran Air was forced to cease many of its international routes and could no longer purchase new Airbus or Boeing aircraft for the past several decades due to tension between governments. However, on January 16 2016, sanctions against Iran civil aviation were lifted after Iran implemented the JCPOA (Joint Comprehensive Plan of Action) regarding its nuclear program. This was a major breakthrough for Iran Air, who were looking to replace their outdated fleet of Airbus A300’s and Boeing 747-200’s (with an average age of around 30 years) but could not due to sanctions. Just in the past week, Airbus accepted an order from Iran Air for a total of 118 aircraft following a visit by Iranian President Hassan Rouhani to France. The order consists of 21 A320’s with the current engine option (ceo), 24 A320’s with the new engine option (neo), 27 A330ceo’s, 18 A330neo’s, 16 A350-1000’s, and 12 A380-800’s. The total value of the deal is around 25 billion US dollars. Airbus has also agreed to assist with pilot and maintenance training for the new aircraft. Iran will also receive help upgrading its civil aviation infrastructure, including aerial navigation systems.

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