Investigators from the National Transportation Safety Board have recovered a cockpit voice recorder from the primary crash site where a Learjet collided with a busy roadway in South Florida last week, killing all nine people on board.
When you fly an airframe at higher than intended altitudes there is a shift in the actual force of air flowing over the wing.
Wings need airflow over the wing to generate lift, and you can induce a stall in enough airflow over the wing even going very fast, if high enough.
Worse, there are speed limits to the airframe design, and as you go higher the stall speed and the overspeed speed become closer and closer together. The way the jet was flown these parameters would have been within a few dozen KPH of another.
A bank or turbulence or small deviation could then easily push the aircraft into either limit and past it.
When this happens loss of control can occur due to buffeting or ovulations of the control surfaces in an overspeed event. An original stall at too high an altitude could cause a loss of altitude but increased speed at a high angle of attack, again creating overspeed conditions with nose down.
The result in either limit being exceeded results directly in a follow on overspeed that rips the rear of the airplane control surface off, making recovery and flight impossible.
This is a classic and well defined flight parameters problem.
as you go higher the stall speed and the overspeed speed become closer and closer together
fascinating!
it’s been a long time since I exercised my pilot cert so I’m very rusty with my aviation science, but I’d’ve guessed that lower air density meant less drag and less stress on the airframe, and I’d have assumed that the wings losing lift from too little air flow would correlate pretty closely with the forces that cause overspeed
how does it work that an airframe’s max rated airspeed doesn’t change at the same rate as a level flight stall speed?
When you fly an airframe at higher than intended altitudes there is a shift in the actual force of air flowing over the wing.
Wings need airflow over the wing to generate lift, and you can induce a stall in enough airflow over the wing even going very fast, if high enough.
Worse, there are speed limits to the airframe design, and as you go higher the stall speed and the overspeed speed become closer and closer together. The way the jet was flown these parameters would have been within a few dozen KPH of another.
A bank or turbulence or small deviation could then easily push the aircraft into either limit and past it.
When this happens loss of control can occur due to buffeting or ovulations of the control surfaces in an overspeed event. An original stall at too high an altitude could cause a loss of altitude but increased speed at a high angle of attack, again creating overspeed conditions with nose down.
The result in either limit being exceeded results directly in a follow on overspeed that rips the rear of the airplane control surface off, making recovery and flight impossible.
This is a classic and well defined flight parameters problem.
fascinating!
it’s been a long time since I exercised my pilot cert so I’m very rusty with my aviation science, but I’d’ve guessed that lower air density meant less drag and less stress on the airframe, and I’d have assumed that the wings losing lift from too little air flow would correlate pretty closely with the forces that cause overspeed
how does it work that an airframe’s max rated airspeed doesn’t change at the same rate as a level flight stall speed?