Nothing is more imminent than the impossible. Victor Hugo
Early during pilot training, engine failures are thought. The rudiments of forced landings are learned, single engine aircraft obliges. The total experience acquired for the newly licensed professional pilot is equivalent to 4 or 5 hours on a light aircraft. According to authorities, this total is quite sufficient for the rest of a pilot career in order to master this complex manoeuvre. Once licensed, a pilot will never see formal total engine failure training events other than personal practice of the procedure’s memory items specific for single or multiengine. It must be known that no training is required for multiengine total engine failures.
The industry considers a pilot an expert in this matter as it sweeps under the carpet of indifference all the arguments better known as human factors.
Total engine failures are statistically a rare event. However, experience demonstrates that total engine failures occur regularly in the air carrier world *. Here are a few examples :
- June 1982, a B-747 in Indonesia (volcanic ash ingestion)
- July 1983, a B-767 in Manitoba (faulty fuel management)
- December 1989, a B-747 in Alaska (volcanic ash ingestion)
- August 2001, an A330 in the Azores (fuel leak, faulty fuel management)
- January 2008, a B-777 in London (fuel system icing)
- January 2009, an A320 in New-York (multiple bird strikes)
- November 2016, an RJ-85 in Medellin (faulty fuel management)
The total number of those incidents/accidents is much greater, all categories. The statistics are stated from more or less democratic countries. General aviation events* are categorized as engine failures with no distinction between singles or multis.
The main cause of total engine failures is clearly fuel management issues or fuel system failures and management. The second being the ingestion of environmental matter : Hail, icing, intensive rain, volcanic ash and unfortunate feathered creatures, followed by human factors at large and mechanical failures.
Sadly, many events result in numerous fatalities.
Facing a total engine failure and within a very short time-lapse, the required piloting and airmanship becomes very crucial. At the onset, the stunning surprise («startle effect») neutralizes a few precious seconds particularly during take-off. Work load, procedures and communications rapidly saturate piloting efforts.
In the cruise phase at a comfortable altitude, time will permit more sustained effort for a restart of at least one engine.
Flying a single engine aircraft, pilots normally should demonstrate good situational awareness (SA) at lower levels than multi engine pilots. It is hoped that glide distance is known, equally options for aerodromes or usable fields. Nothing is expected of multi engine pilots.
It is recognized that multi engine pilots have less SA for such a drastic failure. Better review the rational. For a light twin one engine failure, this corresponds to a loss of 50% of power initially available but it coincides with an 80% reduction of climb performance. The combined factors affecting this reduction in performance are the loss of slipstream over the wing, the increased drag caused by flight controls deflection, non coordinated flight and windmilling propeller. However significant, airframe condition (paint or lack thereof, dents, dirt) and propeller degradation are not considered in section 5 of the AFM. To continue climbing at the maximum certified gross weight becomes problematic if not impossible. The old saying that the second engine will take you to the accident site rings a bell.
An Australian study (2005) indicates that it is more likely to suffer fatalities from an engine failure in a light twin during take-off than in a single engine. The main causes are loss of control and «stubbornness» attempting to maintain level flight in an aircraft that cannot do so under the prevailing average conditions. In such a scenario, good SA will show that one is facing de facto a total loss of power.
Single engine performance of modern medium turboprop carriers is not an issue. Turbojet are of course in a class of themselves.
Another important element to consider: an engine failure is much more likely to occur when the engine is developing full power.
Mental preparation and procedures
Mental preparation prior take-off becomes an essential asset: a briefing appears indispensable. Certainly, it can be argued that take-off briefings become a never ending litany of procedures. Nevertheless, good flight discipline requires a review of the options available and the neighbouring geography.
At low altitude, time becomes a constraint. Priorities must be structured:
- Understanding the possible imminence of a total loss of power in order to reduce the surprise (startle effect).
- Recognizing the failure.
- Proceeding immediately with the procedure :
- Optimum glide attitude : «Everybody nose down»!
- Checklist : AFM memory items.
- Select an appropriate landing site : altitude permitting, a runway otherwise a field or an obstacle free area.
- A brief emergency call
- Engine restart attempt, never compromising gliding precision.
- Securing procedure.
- Cabin preparation.
The impossible turn
Flight manuals generally require a minimum of 800 feet for a single engine aircraft to return to the runway. Many will call this manoeuvre «the impossible turn». It is worth noting that a return to the runway behind requires much more than a 180° turn.
At the other end of the spectrum for an A320, in ISA conditions, calm winds, carrying 80% of the maximum certified load, a return for landing on the departure runway in the opposite direction will require 3100 feet. An A330 that number is 2200 feet: have you seen the wings on that thing ? What is the cost in altitude for your airplane? With this in mind it could be easily argued that a sort of decision altitude can be established to help alleviate the startle factor and improve the decision making process.
At this point we cannot bypass the flying excellence and superior judgment exercised by the US Airways 1549 crew in January 2009. The captain, a licensed glider pilot, rapidly established that it was impossible to return to his departure point or to reach one of the many neighbouring airports.
A valuable tool to improve SA is to understand the aircraft’s glide ratio. Glide ratio is defined as the distance that an aircraft can cover for a specified altitude at optimal glide speed. This distance is of course influenced by wind component, aircraft weight and drag as opposed to the ideal profile. Under gliding condition, the greater the weight, the further glide distance will be. The optimal ratio will occur at a greater speed. The sink rate will be indeed greater, however so will be the optimal glide speed.
Wind must also be known. A no-brainer exists for tailwinds. Turning downwind to reach a runway wherever located, is a great bonus. Technology in the form of FMS or iPad software here is an absolutely required SA tool. For a headwind, of course glide distance will be reduced. Speed must be increased by a certain amount to improve glide distance. Of course sink rate will increase.
The extreme example is the case of a 60 kt headwind encountered for a glide speed of 60 kt. The aircraft is going nowhere fast! Increasing airspeed, clearly, will improve groundspeed and distance covered. This condition is not linear. A good rule of thumb is increasing glide speed by 10% will improve glide distance.
A final point must be understood : always fly the aircraft until immobilized. Pulling on the nose in the futile attempt to stay airborne longer, tough very instinctive is immeasurably fatal. Glide distance will be reduced. Initially the aircraft remains airborne while the airspeed bleeds back. At this point stall will become imminent at a height where consequences become disastrous. Stalling at 100 or 50 feet will cause more damage than touching down under controlled flight on any surface.
The following table shows different glide ratios for different types. It is worth noting that the numbers are for factory new aircraft, clean and without any surface degradation. Atmospheric conditions are standard and calm.
|Albatros (yes, the bird)||24 kt||22 :1|
|Paraglider||25 kt||12 :1|
|Cessna 172||82 kt||12 :1|
|PC-12||114 kt||15 :1|
|B767||210 kt||19 :1|
|A320||200 kt||21 :1|
|Average glider||55 kt||40 :1|
Wind will greatly affect glide ratio along with air vertical movement via thermals and it’s evil alter ego: downdraft. Other vertical motion originating from wind flowing against geographical feature (ridge and orographic systems) will have their say.
Pilot judgment, again
Finally, on the subject of glide ratio, nothing equals pilot eye judgment, especially in the last thousand feet. The precise faculty to determine glide termination (that point that remains fixed in the windshield, not the eventual touchdown) requires practice and definite ease. A «motor» pilot becomes in many ways desensitized by the necessity to use the throttles / thrust levers to correct fixed 3° approach paths. Glider pilots develop and train every day the skill to evaluate an approach without any possibility of adding power. Excellent safety is attained while flying gliders.
The industry would gain very much in flight safety by integrating in its regular training programs total engine failures manoeuvres. The counter argument is cost in a continuous drive to reduce expenses of corporate and governmental worlds. Cost of progressive flight safety will never bring value to shareholders.
* Statistics may vary from one country to the other.