ACT is one of the 3 letter abbreviations worth remembering. It has 2 important meanings for pilots:
- ACT: Altitude – Configuration – Thrust
The challenges with ultra short high altitude runways in Nepal was of course a challenge which demanded airmanship at a high level. First and foremost was the will and skill to fly safe. This included ability to pilot the Twin Otters close to and sometimes at the edge of their performance limits, but never beyond. Insight in high altitude mountain flying, local weather phenomena combined with the limitations of each STOL port. It has been too many accidents and I am confident that many could be avoided with stricter understanding, skills and discipline.
The Will and Skill to fly safely can never be overestimated.
As mentioned several of the Nepal STOL ports where not long enough to meet the ICAO STOL requirements. This mainly due to the terrain which didn´t allow the construction of STOL PORTs according to the standard criteria at many places. It was simply impossible to build a long enough runway in Himalaya. The most known sample is Lukla, the gateway to Everest. That many of the STOL Ports where at a high altitude with thin air and a hot climate parts of the year added to the problems. This is due to the fact that flying in thin air demands higher speeds in take-offs and landings, while at the same time the engines produced less power. This was partly compensated by the construction of the Pratt and Whitney PT6 engines which was used on the Twin Otter Aircrafts. The PT6 engines which were «Flat Rated», i.e. they had more power at altitude than other engines. The downside of this was that the engine used more fuel at low altitudes. This was not a big issue in Nepal, where most of the flights were at relatively high altitudes.
We are soon going to add pictures and videos to our blog! 🙂
The minimum speed required to be able to control a multi engine aircraft is the most critical engine fails is called Minimum control speed which has the ICAO standard abbreviation: VMC, meaning Velocity Minimum Control. The normal standard requirement in any commercial flight operations is that a runway is long enough so that the airplane can abort the takeoff run and stop on the runway before reaching VMC. In addition the aircraft should be able to climb above any obstacles during climb out. There are of course some margins regarding take of length and obstacle clearance in addition considering weather and runway condition and some leeway with regard to pilot handling. This is all described in the ICAO STOL manual. More details later.
Some of the Nepal airports could not meet these requirements due to terrain and hence didn´t meet the ICAO requirements. The runways were so short due to the surrounding terrain that take-offs had to be done without the ICAO standard. There were basically 2 ways: 1. Lift-off below VMC and hence having the risk of an engine failure below VMC when airborne which could lead to loss of control, i.e. that the airplane would flip around, or; 2. Lift-off at or above VMC and hence not having enough runway to stop if an engine failed late in the Take-Off run.
We did find ways to mitigate the above risks to an acceptable level, more to come!
«A mile of road gets you nowhere, a mile of runway can get you anywhere” is an old aviation proverb. It is only partly true since less than half a mile is enough to operate a STOL airplane.
STOL means Short Take Off and Landing. A STOL Port is hence an airport designed for airplanes with STOL capability, i.e. that it can take-off and land shorter than normal aircrafts. The STOL ports are most often built where a regular airport cannot be built due to terrain limitations, or other operational limitations like close vicinity to populated areas. STOL ports can also be built specifically in a network of STOL operations to provide remote areas or smaller communities with the advantage of having an airport. Norway built 30 STOL ports in the Western and Northern regions in the sixties. with daily scheduled routes with Twin Otter aircrafts operated by the Airline Widerøe. The Norwegian STOL port standard was 800 meters long runways, which were suitable for the De Havilland Twin Otter airplanes in uses then. It was long enough to meet the requirement of Take-Offs with a speed which allowed full control if an engine failure on the most critical engine occurred. Below that speed an engine failure would lead to loss of control as the aileron and rudder did not have enough airflow to counter for the yaw / roll caused by asymmetric trust from the live engine and drag caused by the propeller on the “dead” engine.
The STOL ports was rated in 3 categories A, B and C, as we did in Norway. A was regular STOL ports without any specific challenges. B was more demanding with some challenges when taking off or landing or other restriction with regard to runway length, conditions or altitude, approach or climb-out. Both A and B STOL-ports could be flown both ways i.e. landings and take-offs could be performed both ways, depending on wind conditions. A C-port was the most demanding a could have multiple challenges with regard to runway length, profile, elevation and obstacles. Most of them would be so called «one way in, the other way out», i.e. approach and landing could only be from one direction and the take-offs would be done in the other direction. The most famous airport was Tenzing Hillary Airport also known as Lukla which is rated as the most dangerous airport in the World. It was the gateway to Everest Base Camp with a lot of activities. Personally I would not call any airport «dangerous», but rather «extremely challenging». Lukla was indeed extreme and challenging as proven by quite a few fatal accidents and near misses throughout the years. Add to that extreme commercial pressure. See a 3 minutes teaser or our 1:05 hr video on Vimeo:
Flying in the Himalayas, with the terrain above me! That was a challenge I could not resist. I applied immediately for the job, got an interview and soon after acceptance. My employer Widerøe Airline, was positive and a leave without loss of seniority was accepted. My wife Wenche accepted also even if she was pregnant with our third child. A boy was born and away I went with Wenches blessings. Just 2 months later she and the 3 children was with me in a nice home in Katmandu. I was checked out on the STOL ports and ready to take over from my predecessor Captain Don Lelievre, a French Canadian.
This adventure started for me in 1985. I was a Twin Otter Captain in Widerøe Airline in Norway. Widerøe was a domestic airline which connected the Norwegian STOL ports with National domestic and international airports. We where told that they at the time was the Worlds largest Twin Otter operator. The STOL ports covered the west coast mid and northern Norway. The flying was demanding with VFR/IFR operations in fjords an mountainous terrain.The weather was often extreme. The Twin Otters was scarcely equipped, there was no autopilots, weather radars or ground proximity warning systems. The ground equipment on the STOL ports were equally basic with non precision approaches and basic lightning. All this prepared us well for the Nepal STOL mission. When ICAO contacted Widerøe and asked if any pilots would be interested in flying the UN plane in Nepal, they clearly stated that this was due to De Havilland’s recommendation.
As I have written about the What, Why, How and When´s and my views on Airmanship, I will now turn over to the practical and maybe ultimate sample of what this is all about. I will write about our STOL mission in Nepal in the mid-eighties where we flew on some of the most critical airports in the World. I use the word critical instead of dangerous as I truly believe that all these airports can be operated on within acceptable safety criteria. I do not subscribe to such terms as «The Most Dangerous Airport» in the World, etc. this is often credited Lukla, also known as Tenzing Hillary Airport. There is no doubt that Lukla and other airports in Nepal are some of the most critical airports in the World. After all it is unusual that most of the flying is done with the terrain above you instead of below you. In such a critical environment we rated the airports in 3 categories: A – B- C. A was the “easiest” ones, while C the most critical. Note that all the mountain airports where STOL ports, i.e. Short Take Off and Landing fields, which demanded precision flying. The proverb: “Any runway gets to short if you land in the wrong end!” has a special and significant meaning there.