Expected Fuel Flow would also work to serve as a good indicator of thrust, good crosscheck
AirFlorida may have been saved if the pilots did that.
Refer to Post 4. While I agree with the point of fuel flow check, from personal experience I can say that when such an event tales place such as the Air Florid Potomac crash, the PF tends to only glance at the engine gauges of EPR early during the takeoff run. There is no way in my experience the PF could closely check the fuel flow and make a meaningful assessment that the needles would have shown it to be even slightly below the expected figure even if the correct fuel flow for the power was present.
There was snow on the runway during the Potomac accident so keeping straight on the centreline on a slippery runway would have been an absolute priority by the captain even if he could distinguish the centreline under the snow. Assuming for the sake of argument the captain is PF, his total concentration is on the runway centreline and correcting quickly for the slightest deviation - especially if any significant crosswind exists.
Any glance at the engine instruments by a PF is a quick glance of one second maximum then back to the centreline. Providing that glance sees EPR and N1 for both engines are all parallel and there is no sudden pull to one side signifying a significant thrust imbalance, then he will assume operations are normal. That is true for a night takeoff as well where the cockpit lighting is low. The PM is watching two things. Firstly that the aircraft is going straight down the runway and secondly a glance at the engine parameters. if the needles of each engine are all parallel as expected he too assumes there are no discrepancies. It is only when you see a significant split between both engines that alerts either pilot to a problem.
I had two incidents where in each case on the takeoff roll the copilot noticed a sudden large split between the EPR and called out. The first occasion was at 30 knots. I had felt no swing and the aircraft was accelerating normally. I hadn't even looked at the EPR at that low speed because I was concentrating on the the centreline. As soon as the copilot called my attention to the split EPR I looked and saw one at 2.10 EPR and the other at 2.24 EPR. The takeoff was rejected at low speed and the aircraft taxied back for investigation by maintenance. OAT was 30 degrees C it wasn't icing..
The second event was more disturbing. Around 100 knots the copilot called something about "overboosting on No. 2" and tried to pull back the No 2 thrust lever from under my hand. There had been no swing. I glanced at the N1 and both gauges showed equal readings of 100%. In other words there was nothing wrong with the engines. By holding firmly to both thrust levers I was able to stop the copilot from continually trying to drag back the No 2 thrust lever as he was convinced the engine was overboosting.
I said "Set N1 at 100%" and still he tried to over-ride me on the thrust levers despite both N1 showing correct at the planned 100% N1 for the P&W JT8D-17 engines. During the climb the problem fixed itself and the No. 2 EPR returned to the expected figure.
EPR as a primary thrust parameter is fine in theory but when it has been known to give an occasional erroneous reading, one starts to be wary of trusting it implicitly.
Last edited by Centaurus; 23rd Jul 2020 at 09:51.