Comment by cpgxiii
2 days ago
The F-16 EPU is to keep the flight controls powered so the plane doesn't immediately become uncontrollable following engine failure. The EPU doesn't provide thrust of any kind.
The 787 and nearly every other commercial aircraft with powered flight controls [1] (fly-by-wire or traditional) has emergency power available via RAT and/or APU, and any fly-by-wire aircraft has batteries to keep the flight control computers running through engine failure to power supply being restored by the RAT and/or APU. Due to its unusually high use of electrical systems, the 787 has particularly large lithium batteries for these cases. There is no need for an additional EPU because the emergency systems already work fine (and did their jobs as expected in this case). You just can't recover from loss of nearly all engine thrust at that phase of takeoff. [2]
1. The notable exceptions to having a RAT for emergency flight controls are the 737 and 747 variants prior to the 747-8. In the 747 case, the four engines would provide sufficient hydraulic power while windmilling in flight and thus no additional RAT would be necessary. The 737 has complete mechanical reversion for critical flight controls, and so can be flown without power of any kind. There is sufficient battery power to keep backup instruments running for beyond the maximum glide time from altitude - at which point the aircraft will have "landed" one way or another.
2. There is only one exception of a certified passenger aircraft with a system for separate emergency thrust. Mexicana briefly operated a special version of the early 727 which would be fitted with rocket assist boosters for use on particularly hot days to ensure that single-engine-out climb performance met certification criteria. Mexicana operated out of particularly "hot and high" airports like Mexico City, which significantly degrade aircraft performance. On the worst summer days, the performance degradation would have been severe enough that the maximum allowable passenger/baggage/fuel load would have been uneconomical without the margin provided by the emergency rockets. I'm not aware of them ever being used on a "real" flight emergency outside of the testing process, and I think any similar design today would face a much higher bar to reach certification.
> at which point the aircraft will have "landed" one way or another.
Ah
Also we need more rocket thrust takeoff airplanes.
> the maximum allowable passenger/baggage/fuel load would have been uneconomical without the margin provided by the emergency rockets.
Your momma so fat…
But seriously, is there a commercial aircraft that can’t climb on only engine?
That is a somewhat complicated answer. The simplistic answer is that certification criteria require all turbine aircraft (turboprop or jet) to meet minimum climb performance following an engine failure at the worst part of takeoff. Multiengine piston aircraft (almost all of which are grandfathered in under prior rules anyways) are not required to do so. As a proportion of commercial passenger aircraft, multiengine piston aircraft are fortunately fairly rare in terms of passenger-miles flown, but they are still fairly common in certain markets.
However, that answer is hiding a lot of complexity. In a multiengine turboprop, single-engine climb performance is dependent on fathering the propeller of the dead engine(s); if you don't (or can't), you will probably crash.
In all aircraft, different takeoff conditions (ambient temperature, pressure, runway length) will result in different performance (maximum takeoff weight, runway length and takeoff thrust required). In some extreme conditions (e.g. "hot and high" airports like Mexico City or Denver) this can result in a reduction of maximum takeoff weight to ensure that engine-out climb performance is maintained. Generally aircraft used in these airports are designed and/or acquired with these conditions in mind, and thus the aircraft are still profitable to operate with the reduced MTOW.