The "single" Multi -engine aircraft

Many people consider that two is better than one. In fact a light twin has much more performance is more spacious and thus is more comfortable for passengers than a single one.

Nonetheless, and as Richard N. Aarons says, while single-engine aircraft may not be safer, twins can be more dangerous. I do agree when they are not operated correctly - of course - and when an engine is out at or close Vr in a hot day with full load. 

When we lose one engine on a twin, performance is not halved, but actually reduced by 80 percent or more.This 80-percent performance-loss is not just a number, as we can easily demonstrate. And It's easy to explain this.

Let's consider that a  light twin which has an all-engine climb rate (sea level, ISA, max gross weight) of 1,600 fpm and a single-engine climb rate under the same conditions of 300 fpm, the loss of climb performance in this case is:

100-[(300/1600) x 100)]= 81,3% 

The climb performance remaining is 18,7.

To achieve a 100/200 fpm single engine RoC after Vr one must comply at least with 5º bank to the live engine side ("raise the dead"), the dead engine immediately feathered and the aircraft "clean".

Considering a hot day at MTOW flying a twin with a rough and tear fuselage (that increases even more the drag) for sure we will not have a positive rate. When possible, taking off with Cowl flaps closed can give an extra 30-50 Fpm and this sometimes can make the difference....

I do consider it's better to hit a fence trying to land (on this circumstances), have some minor repairs to aircraft and walk away without injuries, than attempting with the impossible take-off.

Some time ago a PA31 chieftain was climbing through 9000 Ft when one engine flaed out few time after having departed. It  was not able to return to the airport, crashing very close to the Rwy. On this situation the bad management of the energy and procedures were the cause of the fatal crash. It will be discussed on the next post.

The next table* shows some performance losses for twins with one engine out:

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Colgan Air 3407 - Buffalo

As I've referred in the BALPA's post, today I share the history of the Colgan Air flight 3407. This event is in line with what is said by the British Association.

The history of the flight...

On February 12, 2009, about 2217 eastern standard time a Bombardier DHC-8-400 (Q400), operating as Continental Connection flight 3407, was on an instrument approach to Buffalo-Niagara International Airport (BUF), Buffalo, New York, when it crashed into a residence in Clarence Center, New York, about 5 nautical miles (nm) northeast of the airport. The 2 pilots, 2 flight attendants, 45 passengers aboard the airplane were killed and also one person on the ground.
 

For me the main reason for the crash was "captain’s inappropriate aft control column inputs in response to the stick shaker caused the airplane’s wing to stall."

This is just another proof that sometimes the basics of flight training are not put in practice for a stall recovery. Just like the case of the Airbus 330 performing the Air France flight 447. Similar nose up input to the sidestick was given as response to a stall. That make us wonder. Did those crews realised of the stall sate? I guess no..

Also the fatigue may have contributed to the events since pilots didn't have proper spaces to rest. As NTSB says "the pilots’ performance was likely impaired because of fatigue, but the extent of their impairment and the degree to which it contributed to the performance deficiencies that occurred during the flight cannot be conclusively determined."

•  Bombardier Q400 PFD/  Air Speed indications

 

 Fig 1. - NTSB Q400 PFD explanation

A low-speed cue is shown as a red and black vertical bar that extends from the bottom right of the vertical scale. The low-speed cue warns pilots of an inappropriately low airspeed for the airplane configuration or operating condition. If the airplane’s IAS is less than or equal to the IAS at the top of the low-speed cue, the stick shaker activates. Also, the numbers on the IAS display change from white to red, providing pilots with another visual warning of an inappropriately low airspeed.

NSTB Animation:

"Good judgement comes from experience. Good experience comes from someone's else bad judgement."

Learn from others' mistakes.....as we won't live long enough to make ours all of them.

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Microburst

The Microburst is one of the most dangerous weather hazards. It consists of air streams descending from the CB's clouds at a speeds that can reach 60Kt, spreading omni-directionally at the surface. They can last up to 5 minutes to dissipate. Generally they have a 4 Km diameter.

When an aircraft encounters a microburst, the IAS increases due to the increasing of the headwind (1), then experiences a downdraught (2) and finally a tailwind (3).

The microbursts can be described in two groups:

1. Wet microburst: A lot of precipitation associated. The magentas can be well depicted on the weather radar.
2. Dry microburst: It's more difficult to identify since the precipitation has evaporated before reaching the surface level.

Here is one animation of a microburst:

• Large aircraft coping with this phenomena

A sudden loss of speed associated with low altitude on the critical approach phase can be fatal for large jet aircraft in the case this microburst phenomena is not recognized and if all actions are not taken in due time by the crew. The time since the flight crew realizes this hazard with the additional one necessary to take the actions and speed up the aircraft may not be sufficient.

The most practical example of a microburst was the crash of the Tristar L1011 of the Delta Flight 191 at Dallas-Fort Worth International Airport on 2nd August 1985.On the following clip are the last two minutes of the flight.

Have anyone here ever experienced such similar event successfully ?


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