2StgTurbine

Easier said than done. Even with modern manufacturing it is impossible to produce identical turbine engines. Microscopic defects (caused either during the manufacturing process or routine maintenance) will affect the true failure point of an engine.

rickair7777

Not expecting an absolute guarantee, just an informed, calculated risk.

JohnBurke

Again, with the exception of those engines that contain electronic limiting (eg, FADEC, etc), you can't trim the top. end of a turbine, and the acceleration isn't linear; it becomes a very steep upward curve to destruction when at the upper end of the power spectrum, which is why we do derated takeoffs and why it's important to respect the numbers.

Kalitta's engines in Bogota had no margin in them; Kalitta cobbled them together out of red tagged parts bought from various airlines and they were already beyond the margins of safety and legal tolerance. That they came apart when pushed was no surprise.

There's a military mentality that one would like to have military power available in a non-military aircraft, but the limitations, design, and criteria for the aircraft are quite different. Many platforms already have an excess of thrust, up through aircraft that are already 1+1, etc, and the ability to derate and still have adequate thrust available to call "military" is an option. This is not the case on most transport category aircraft, and unlike the tactical taxis, transport category aircraft lack bang seats. There is no returning it to the taxpayer.

There are also no taxpayers. Only shareholders.

MaxQ

Hi John
Thanks for the informative post. Kudos.
I would add the additional that from very early on pilots are taught that “there is a huge safety margin built in”.
Needless to say some routinely go a little beyond because..well this huge safety margin that has been taught. I suspect 100% of those that want “a little bit more” are positive no harm will come of it.
Your post is an excellent reminder of the reality of component fatigue.

ptarmigan

All of these are real considerations, however it really does not change the premise. I am close enough to the cert part of the industry to have a little insight into it...

takingmessages

Years ago I witnessed the aftermath of a midair collision between a Navajo and a Turbocommander 1000. Both aircraft sustained substantial damage, but both landed safely with the pilot of the Navajo sustaining minor (rather minute) injuries. A four-stitches cut in his neck...

I was a fairly close friend of the Turbocommander's pilot and had the opportunity to inspect both aircraft at my leisure shortly after the event. I was a private pilot at the time and had been wandering around airplanes for years, although I wasn't (and I am not) a mechanic.

The airfield involved was this half-and-half military-civilian airport where you ONLY operated eastbound. Unless, well...
Unless you hit another aircraft mid-air.
The Navajo was inbound from the South about to cross the extended centerline to initiate a left downwind, when it hit the Turbocommander that had just taken off and turning right to head South. Although I never heard the radio transmission, rumor has it that the conversation between the Navajo and the tower went something like this:

TOWER!!!
I HIT SOMETHING!!!
I AM LANDING WESTBOUND!!!

Did you hit a bird?
Can you circle to the other runway?

NOOOOOO!!!
I DON’T KNOW WHAT I HIT!!!
I AM LANDING!!!
ROLL THE FIRETRUCKS!!!

And he landed...
Not the best thing he could have done, but the ONLY survivable option he had.
We saw the airplane land westbound and wondered, oh boy, somebody had an emergency. The airplane slowed down and did a 180 in the runway. That's when we saw the gaping hole in the right side of the airplane. It looked like someone grabbed a gigantic can opener and ripped the roof open from the copilot windshield all the way to the first window over the wing. The right prop had one blade smashed and out of sync with the other two. The vertical stabilizer was all bent and smashed up. The rudder was gone.
What a mess...

The guy then taxied to the fire department building.
How convenient, work from home...
Some firefighters pulled the pilot bleeding from the cockpit while another one pulled out the winglet of the Turbocommander from inside the fuselage.
Nobody knew where (or whom) the other aircraft was.

The Turbocommander landed shortly thereafter on another airport some 50 miles to the South. A couple of hours after the Navajo landed, the pilot was back in the cockpit picking up his stuff (with a white medical patch in his neck) when this little car came to a screeching halt in the parking lot, and my friend Jorge Paredes came out very obfuscated asking where the pilot of the Navajo was. The guy answered from the inside that he was it and Jorge told him "I am the pilot of the other aircraft!".
And that's how they met and shook hands for the first time:
with their arms reaching each other out through the hole in the fuselage of the Navajo.
How surreal...

After hours walking around both aircraft, I could reconstruct the obvious impact sequence. The airplanes hit each other head on. The right wing of the Turbocommander scratched the top of the nose of the Navajo until it hit the windshield right next to the mid-pilar. It blew up the right windshield, the instrument panel, the copilot seat and ripped apart the fuselage up to the first 2 passenger seats. Then the right prop of the Navajo severed the wing of the Turbocommander leaving approximately a couple of feet of the right aileron hanging attached to the wing. There was a small 1-by-2 inches triangle surgically cut from the trailing edge at the wingtip of the Navajo. That was cut by the blade of the Turbocommander on the way out.
And severely damaged the right turbine...

When the right engine of the Navajo severed the right wing of the Turbocommander, the big chunk of wing hit the vertical stabilizer of the Navajo significantly deforming it and detaching the ruder. The Navajo pilot survived because immediately after the collision he pulled the power from both engines and made a 90-degree left turn within gliding distance to the runway. I guess that I don't have to elaborate on control issues with a dead engine and no ruder. Never mind a broken windshield, a destroyed instrument panel and a gapping hole in the fuselage...
The Navajo glided back to Earth just like a paper airplane would have...

I don't remember how big the chunk of missing wing from the Turbocommander was, but feel free to fit it from mid inside fuselage of the Navajo all the way to the right engine. It was big enough to severely unbalance the Turbocommander.
And this is where this story fits this thread...

A few days later I got to talk to Jorge and hear the harrowing story first hand. His account went somewhat like this:
"I had just completed the right southbound turn and changed frequencies when I heard a 'tud', the aircraft shuddered and initiated an uncommanded turn to the right. I didn't' know what was happening (he could not see the right wing beyond the engine from the cockpit, so he didn’t know he was missing a big chunk of wing), so I applied full left aileron and rudder and reached for the engines to cut the left one and set the right to full power. That's when I saw all the temperatures in the right engine going off the charts, and I knew that it was going to blow up (remember the little triangle?). From that point on I flew with the left engine idle and praying that the right engine would hold until we landed, because I knew that if that engine quit we were dead. The engine died a few minutes later right at touch down."

Both aircraft were repaired and flew again.

The moral of the story is that Jorge and his passengers survived because he abused his engine unmercifully.

Finally, I am neither advocating nor discouraging one thing or another, I wrote this story here because I think it relates and it is such an unusual memory that I think it deserves to be preserved.

Thanks for reading and I hope that you enjoyed it...