1950’li yıllarda ABD Federal Sivil Havacılık Örgütü (FAA), olagelen bazı hava olaylarına dayanarak, 2 ve 3 motorlu hava taşımacılığı kategorisindeki yolcu uçaklarının uçuş planlamasına bir kısıtlama getirdi.

Bu kısıtlama özetle şu idi: Yol boyu (acil iniş) ve varış yedek meydanı olanaklarını,“tek motor uçuş rejimi ile“, 1 saatlik bir yarıçap içine sığdıramayan remote meydanlara uçuşlar, uçuş emniyet değerlendirmeleri ile yasaklanmıştı.

Özetle 2 ve 3 motorlu uçaklar uçuş yolu boyunca, bir motor arızasındaki uçuş rejim ve seviyesinde, daima, 60 dakikalık bir mesafede uygun bir acil/yedek meydan bulunduracak şekilde yol planlaması yapabilecek, aksi halde uçuş izni verilmeyecekti.

Başlangıçtan itibaren 4 motorlu uçakların dışında tutulduğu uzun menzil çift motor harekat usullerine, ismi uyuşmasa da (Extended Twin Engine Ops) 3 motorlu uçaklar dahildi. Ancak,1964 yılına gelindiğinde, 3 motorlu olan Boeing 727 ve HS Trident yolcu uçak kullanıcılarına ETOPS muafiyeti getirildi.

1980’lerin başlarına gelindiğinde ise, dünya havacılık sanayisinin iki büyük devi; güvenilirlikleri yüksek Airbus A300/A310 ve Boeing 757/767 uçaklarını geliştirmişti. Motor arıza olasılığının gerçekten çok düşük olarak değerlendirildiği bu uçaklar için, bir motor arızasında, kalan motorla güvenli uçuş zamanının 90-120 dakikaya çıkarılabileceği konusu; yapımcı firmalar, FAA ve uzun menzil harekat yapan büyük havayolu işleticileri arasında tartışma konusu oldu. Beş yıl kadar süren müzakereler sonucunda, 1985 yılı, 120 dakikalık güvenli tek motor uçuş süresinin, 2 motorlu bu uçaklara vize verildiği yıl oldu.

Artık, ekonomik 2 motorlu yolcu uçakları, 120 dakikalık ETOPS izni çerçevesinde, okyanus aşırı uçuşlarda, ya da , kara üzerinde olsa dahi uygun acil ve ana yedek hava alanlarının tek motor uçuş rejimi ile 2 saatlik bir yarıçap içinde bulunabildiği varış meydanlarına tarifeli ya da tarifesiz direkt uçuş planlayabileceklerdi.

Bu durum, hava taşımacılığının ticari planlamasında hemen hemen bir devrim niteliği taşıyordu.

Yetki belgesinin alınabilmesi için, ilgilenen havayolu kuruluşları, 12 aylık bir gözetim süresi zarfında konuya ilişkin özel bakım usullerini uygulamak ve belirtilen performans kriterlerini karşılamak durumunda idiler. Hatta birçok havayolu işletmesi, konuyu daha  ileri götürerek, aynı ETOPS özel bakım usullerini, sırf güvenilirliği daha da arttırmak maksadıyla, 4 motorlu uçaklarına da uygulamaya başladılar.

1988 yılına gelindiğinde, çağdaş turbofan motorların güvenirliliğinin önemli ölçüde yükselişinin pozitif olarak saptanması, “yapımcı, işletici ve Federal Sivil Havacılık“ yetkililerini yeni bir ortak çalışmaya yönlendirdi.

Sonuçta, kalifiye olarak değerlendirilen bazı işleticilere, 180 dakikalık ETOPS kriteri uygulanabilmesi konusunda vize verildi.

1995 yılında, 12 aylık gözlem süresinin kısaltılması yönündeki ek çalışmalar meyvasını verdi ve “hızlandırılmış ETOPS gözlem süresi” devreye sokuldu. Bu bağlamda, işleticinin geçmiş ETOPS deneyimi dikkate alındı.

İkinci milenyuma girişle birlikte, Kuzey Pasifik hattındaki bazı direkt uçuş yollarında uçabilmeleri maksadıyla, Boeing 777 uçaklarının, mevcut 180 dakikalık ETOPS kotalarına yüzde 15’lik bir süre daha ilave edildi. Böylece yürürlüğe girebilmiş olan en uzun ETOPS süresi 207 dakika ile Boeing 777 işleticilerinin oldu.

Günümüzde 207 dk.lık bu ayrıcalıktan yararlanan B-777 işleticilerinin arasında; Delta, American, United, Continental, Çin ve Malezya havayolları yer almaktadır.

207 dakikalık ETOPS kriterleri, SSCB’ nin dağılımından sonra hızla globalleşen dünyamızda, yeni kutupsal (polar) hava yollarının 2 motorlu Boeing 777’ ler tarafından da uygulanabilmesine imkan vermiştir.

Şüphesiz, kutupsal yollar diğer konvansiyonel yollardan;

1. Aşırı soğuk statik hava sıcaklığı,

2. Arctic çevre şartları,

3. Yol boyu uygun ve faal yedek meydan mevcudiyeti,

4. Özel muhabere cihazları gereksinimleri, 

5. Özel seyrüsefer cihaz ve usulleri gereksinimleri,

6. Yakıt politikası,

7. Polar bölgelerde, tropopoz seviyelerinin düşüklüğü nedeniyle güneş patlamaları ve Aurora’ nın artan negatif etkileri,

8. ABD yapısı uçaklarda 78N üzerinde harekat için hem FAA’den ve hem de tescilli olunan ülke sivil havacılık otoritesinden özel yetki gereksinimleri, ve benzeri gibi daha bircok açıdan farklılıkları bulunmakta olup bunlar ancak ayrı bir yazı konusu olabilir.

Bu yazıdaki konumuzla Polar yollar arasındaki direkt ilişkiyi doğuran asıl nedenler ise;

    a. 207 dakikalık ETOPS vizesi,

    b. Gelişen teknoloji,

    c. Globalleşen dünya ve uluslar arası iyi ilişkiler olmuştur.

Gelişen ülkemizin, gelişen havacılığına, paha biçilmez “teknik ve yer” ekiplerinin

“olmazsa olmaz”  katkıları ile; güçlü, iyi yürekli, pozitif ve emniyetli uçuşlar dilerim.

HOW MANY ENGINES YOU WOULD LIKE TO HAVE ONBOARD?

(THE ETOPS CONCEPT )

By :  Savaş Uskent

Commander PilotFor my opinion, the award of 207-minute ETOPS criterion for B777 aircraft, is one of the milestones in aviation history as the entry of the new millenium took place.

Although provisional, this was a considerable %15 extension of the previous-180 minute rule.

On the other hand, as Boeing and ALPA concur to increase the provisional limit to 240 minutes, Airbus and Allied Pilots Association prefer to dissent.

Piston engines used in the early days of commercial aviation, were less reliable than today’s modern turbine engines. Four-engine Boeing Stratocruiser was among the airliners to cross the Atlantic.

Back in 1953, two and three engine airplanes were restricted by the FAA from flying on routes that took them more than 60 minutes from an adequate alternate airport.

As outlined in 14 CFR (Code of  Federal Regulations) 121.161:  Unless authorized by the Administrator, based on the character of the terrain, the kind of operation or the performance of the airplane to be used, no certificate holder may operate two or three-engine airplanes (except three-engine turbine powered aircraft) over a route that contains a point farther than 1 hour flying time from an adequate airport, considering still air and one-engine-inop conditions.

Briefly, flight routes for remote destinations unable to include at least one suitable emergency/enroute alternate airfield within a 60-minute radius of one engine out flight regimen were prohibited. From then on, 2 and 3-engine transport aircraft flight planning could be done on the conditions of availability of least one enroute alternate airfield within an hour reach of one-engine-out flight regimen and profile of specific aircraft.

The ‘60-minute rule’, initially limited transoceanic flights to redundant-engine propeller airplanes like the DC-4 or Constellation.

Nevertheless, in 1960s, 3-engine turbine aircraft such as B-727 and resembling British HS Trident were put into service and exempted from 60 minute rule. (The pilot friendly Boeing 727-100 had gone into service in February 1964).

Prudently, considering the possibility of a concurrent rapid depressurization of an uncontained engine failure scenario, most operators would take into account oxygen requirements and lower diversion flight levels as appropriate.

As a matter of fact in 1980s, the two giants of aviation industry had developed highly reliable Airbus 300/310 and Boeing 757/767 aircraft. By 1985, the FAA had accumulated sufficient historical data to conclude that modern twinjets were so reliable that they needed to provide a means for airlines to get around the rule. Consequently, extention of the then present ETOPS criterion was put forward to debate between FAA, manufacturers, major airline companies and related associations. As a result, ‘120-minute ETOPS criterion’ was born, which meant airplanes meeting the criteria could fly up to two hours from an alternate airport.

In 1988, the proven reliability of modern turbofan engines, brought about new sets of discussions to take place. Ultimately, 180-minute ETOPS criterion were guarted to qualified and aspired operators of twin-engine aircraft (1989).

On May 30, 1995, the B777 became the first airplane in aviation history to earn the FAA approval to fly ETOPS at entry into service. On that date, the FAA awarded the Pratt & Whitney-powered Boeing 777, 180-minute ETOPS.

That rule, as a big step forward, had enabled planning of thrifty twin-engine aircraft on direct routes to remote destinations, provided to remain within ”180-minute radius of one-engine-out flight regimen” of at least one suitable airfield.

From my point of view, the new formation of ETOPS criterion was almost a revolutionary step towards modern commercial flight planning and scheduling of air transportation.

To qualify, aspiring airlines had to meet certain performance and maintenance criteria over a 12-month period.

Moreover, several operators have adopted the special maintenance procedures on their 3 and 4-engine fleet aircraft just to enhance reliability and uniformity.

As I cited at the begining of my article, new millenium has added a further %15 extention to then valid 180-minute criterion of Boeing 777 aircraft for North Pacific operations, extending it out to 207 minutes on case by case basis.

Today, there are several major companies enjoying the privilege of 207 minute criterion.

Especially after once-introvert ex-USSR’s hugging with the open world, the 207-minute rule has enabled the rapidly globalized modern world’s companies to plan their B777 aircraft on new polar jet routes, bringing the two opposite sides of the world even closer.

No doubt, polar jet routes differ from the conventionals in some respects such as;

a. extreme cold static air temperature,

b. arctic environment,

c. availability of suitable and operational enroute alternate/s,

d. requirements for special navigation and communication equipments and procedures.

e. Inflight fuel management policy.

f. Increased negative effects of aurora and sun bursts due to decreased tropopause levels and ozone shield over polar regions.

On March the 5th, 2001 Continental Airlines began the world’s first ever daily, non-stop service between New York and Hong Kong flying a B777-200ER. Continental is flying its Hong Kong-bound B777 on a unique new route over the North Pole, Russia and China.

On March the 8th, 2001 Delta Airlines’ B777 completed a demo flight on a polar route from New York to Beijing. The 7,548-mile route, which took the B777 over the North Pole and Siberia, took only 14 1/2 hours to fly.

Moreover, there is a new impetus to extend ETOPS criterion to 240 minutes. As some of the impetus to further extend ETOPS to 240 minutes is being led by Boeing, the dissidents include the ATA (Air Transport Association), ALPA (Air Line Pilots Association), Airbus Industrie and the APA (Allied Pilots Association).

They remain unconvinced whether operating twin-engine aircraft on 240-minute basis on certain routes (as in NOPAC-North Pacific Operations) would maintain the previous safety records of ETOPS. From the standpoint of Airbus, ETOPS in the NOPAC during cold winter months is different to the ETOPS in the NATOPS (North Atlantic Operations).

Therefore, airframe and engine combinations need to be satisfactorily tested under extreme conditions.

From my viewpoint, as far as flight safety concerned, considering contingencies for worst-case scenarios, flying 240 minutes on one-engine-out flight regimen to a remote airport statistically would be safe.

Nevertheless, as far as aircraft components are concerned, 3 or 4-engine aircraft would normally offer a higher redundancy. From a commercial standpoint, operation and maintenance of twin engine aircraft is cheaper. That would mean cheaper air fares and increased passenger and cargo traffic.

As far as in flight occurences are concerned, another factor to consider for long-haul aircraft is a volcanic ash encounter. So far, there have been many incidents of volcanic ash encounter, causing in-flight engine flame-outs, malfunctions or even ultimate engine discards.

Trying to be a logical thinker on a worst in-flight scenario, I am still not convinced that prejudicious opinion of considering 4 or 3 engine aircraft safer as compared to twin-engine operations would be fair.

I believe, just comparison of the number of engines on airplanes would be simple reasoning if you will, and may easily lead to mis-evaluation of the matter. It simply doesn’t make sense to me.

In addition to quality of ergonomics and pilot friendliness of flight decks for contingent emergency conditions under duress, the parameters such as quality, durability, high altitude re-start ability, thrust rate, technical friendliness of aircraft engines, is of utmost importance.

I also perceive a serious problem for high-tech aircraft. In my opinion, safety has somewhat been eroded by highly advanced technology. As manufacturers look for new stuff to sell to their customers, they work hard to invent ergonomic, comfy and safe high tech aviation material such as new types or variants of aircraft, engines,avionics and etc. That is quite natural as they need to survive and their job is to promote the aviation as well.

While new stuff would mean new technical orders, bulletins and unexpected contingencies on initial use of new elements of aviation industry, today’s high technology would mean a take-over of piloting skills, reducing the need for brain storming, causing ultimate loss of basic aircraft handling skills that is indeed a “must have” to cope with all emergency conditions including a concurrent uncontained engine failure and cabin depressurization on an ETOPS flight.

When problems occur the ensuing workload can stretch the limits of two crew members as well. Then comes the crew fatigue and its effect on the flight safety but that is so important on its own and could only be a subject of another article.

As I wear my hat of an experienced pilot and take off the writer’s, I seem to prefer durable, classically steered, twin engine long-haul aircraft. For those I strongly feel as if I can always find a way to keep the bird flying even in the worst-case scenario, just using my uneroded basic piloting skills.

As I change my hat with the writer’s, I seem as if I want to fly on high-tech, redundant engine, fly-by-wire aircraft.

This may sound odd, but believe me the passengers shall make the ultimate choise.

A high-tech 240 minute semi-classical ETOPS aircraft or sofisticated redundant engine fly-by-wire ETOPS exempted aircraft? Time will tell.