These Features Already ‘Departed’ Before United Flight 328 Arrived.

They might augment the probability of surviving apart from the training and ATC.

Nazmi Izwan
7 min readApr 19, 2021
A photo from the ground shows the badly damaged engine on flight 328. Image by Hayden Smith via Instagram.

The news about the United Airlines flight 328 engine failure isn’t foreign for us. Miraculously, there was not a single injured soul on the ground and onboard.

It is not just about luck the plane can safely land back at the airport, it was aid both from the evolving technology and design improvement and also from the skillful set of crews as well as the ATC.

This whole incident has proven the safety design of the aircraft from a technical point of view. Unfortunately, it also shows the limitation on the industry as a whole which still needs some brush-up.

What cannot be ignored was the crews’ accomplishment to handle the situation while dealing with the increasing workload and vibration. Robust training imposed on pilots also can be seen as part of the successful steps in mitigating such emergencies from worsening.

Regardless, everyone is safe and, it is something that has to be applauses.

So, should air transportation that has several high-profile incidents and accidents still proclaimed as the safest mode of transportation?

** This article only aims to deliver contents from a technical side and not from the crews’ action or to bring up any speculation until the authorized investigation has complete.

The Boeing 777 Specification

While all these descriptions may or may not visibly indicates the efficacy of their intended purposes, it shall not be looked away as all of them play such massive and crucial roles in dwindling the impact from an in-flight engine damaged, whether contained or not, particularly in this incident.

1. Fan blade casing

The casing that enclosed the surrounded fan blades provides a containment medium from a rare case of blade detachment. A fan blade weighing says just 15 kg becomes several tons ‘heavier’ because of the centrifugal force acting on it, typically at maximum RPM.

From this force alone, it is like playing Russian Roulette waiting for one of the blades to pierce through the fan case in such a way that it could be catastrophic.

Engine makers such as Pratt & Whitney have to prove to the aviation authority that their engines’ fan blade casing is robust enough to contain a fan blade failure at the highest RPM.

The FAA and EASA counterparts already disclose from their regulations, in this case, the 14 CFR Part 33 and Certification Specification (CS) E respectively, for the engine manufacturer to follow as standard. Here is the statement from the CFR 33.94:

Except as provided in paragraph (b) of this section, it must be demonstrated by engine tests that the engine is capable of containing damage without catching fire and without failure of its mounting attachments when operated for at least 15 seconds

Rather than projecting through the casing like a projectile, a fan blade should and must contain within the engine casing without exiting it. In this way, it cannot damages the adjacent pressurize structure of the aircraft, thus reducing the possibility of explosive decompression.

Although this is neither a Boeing 777 engine nor the Pratt & Whitney 4000, it still shows the casing near the fan blades that are supposed to contain a departing fan blade. Image by Author.

Engine blade casings are made from composite like Kevlar to hold the massive energy from the departing blade.

2. Dry Bay

Commercial aircraft hold their fuel inside the wings. The wings are actually hollow ( minus the metal structure for strengthening and maintaining the shape of airfoil contour ) to accommodate several tons of fuel.

These integral fuel tanks running from the root of the wing until usually one-quarter from the tip, which is why it is a safety feature to have a dry area within a particular section near the engine.

On the Boeing 777, there is a designated area adjacent to the engine that does not carry any fuel and is kept dry. The reason behind this is to reduce the risk of massive fuel leak should any part of the engine, especially the turbines, exiting and penetrating the fuel tank.

The wing dry bay sections on both wings do not hold any fuel inside it as a precaution.

It is one of the risk assessments done on the powerplants to increase the safety level. Thank goodness there was not a single part that was uncontained from the engine for this incident.

3. Thrust Asymmetry Compensation System (TAC)

The system is pretty much straightforward since we could tell from the name itself. When an aircraft fly, particularly during take-off where the thrust is maximum, a sudden engine failure is just as dangerous as it could make the aircraft unstable.

If you could imagine if this happens in the cartoon, it would probably displaying a dramatic spin-off. The unequal thrust needs a countering action to stabilized back the aircraft to its intended course and heading. That is why the Boeing 777s are equipped with the TAC system.

The second the aircraft encounters an asymmetrical thrust, the system kicked in to respond by operating the rudder. The rudder works wonders in eliminating the yaw that in turn decreasing the workload on the pilots.

General description of the TAC system fitted on Boeing 777 from the model’s manual itself.

It operates based on the current condition of the said aircraft, its airspeed, the engine’s thrust and so much more. It is false to assume other aircraft that don’t have this system are not safe. They are all equally safe as the TAC is there only to assist the pilots in maneuvering the aircraft if only an asymmetrical thrust occurs.

4. Single engine operation

One of the requirements for aircraft safety is to engineered a single-engine operation throughout the flight phase. The most critical phase would be taking off. A fully loaded long haul flight definitely demands the highest take-off thrust from both engines to lift off from the ground.

But what if the moment the aircraft has left the ground, one engine suddenly loses power? No need to panic ( it is okay to worry ) as it is capable and certified to fly only with one engine be it in cruising, taking off, or landing.

As you might think that four-engine aircraft are much safer than twin-engines aircraft, then think again. Although quad engines aircraft only lose 25% of the thrust when one engine inoperative compare to 50% for the twin engines, rest assured because it has enough power to keep the aircraft in the air for as long as the pilots need before having to land back as soon as possible.

Simultaneous dual engines flameout is an unusually odd case unless there are external contributing factors like birdstrikes. With the introduction of ETOPS, which stands for Extended Range Twin Engine Operation Performance Standard, twin-engine aircraft are becoming more reliable if not better than the quad.

This regulation set a load of non-compromising rules for the operator and manufacturer to comply with flights flying over the vast ocean by the authority.

It includes monitoring and tracking for any inflight engine shutdown within a particular engine type for a certain period. The rate must be within very low percentages.

5. Technically two fire extinguishers for one engine

It seems logical to have a fire extinguisher for each engine if a fire broke out inside the enclosed engine compartment. What truly matters is that one powerplant can actually get a second Halon gas shot from another extinguisher that is intended for another engine.

Basically, the fire extinguisher bottles are interconnected and have dual outlets for both engines. If the fire does not extinguish after discharging the first bottle, pilots can activate the second bottle to help eliminates it.

Another interesting point is whenever the fire handle to activate the extinguisher for an engine is triggered, it also poses a command to isolate the engine from the airframe.

In other words, all related systems purposely meant to/from that engine will be cut off. The fuel valve will be closed, preventing fuel flow to the engine. Others will be electrical and bleed air.

Air transportation is relatively safe for most parts. All the safety features above are pretty much a tip of an iceberg that is fairly physical. What makes up the underpart of it is those behind the scenes of regulations, maintenance, and training.

This incident did not generalized the whole aviation industry while putting it in the same basket. It gives a big lesson for the whole to eventually investigate, mitigate and improvise the root cause and any slack for that matter, whether directly or indirectly. Sounds cliché indeed but it is a repetitive work that needs to do over and over to enhance the safety of the industry and the flying public.



Nazmi Izwan

Aviation made simple and understandable for general flying public.