Maybe you’re well familiar with the concept of Reduced Vertical Separation Minimum (RVSM) or this is a new area you’re experiencing in the beginning of your career entering the aviation world. In this article I’ve collected the necessary need to know about RVSM and why training in such topic to understand the purpose and benefits. Down below I’ll also share a little story about two experienced pilots who took the RVSM compliance seriously and made the right decision to a safe flight.
As we all know the number one priority in aviation is safety. One of the many aspects of aviation safety is vertical separation, something that was thought of already back in the 1940s. According to ICAO, the vertical separation was 1000 ft in all cases at the time (with a few small exceptions). But in the late 50’s newer aircraft operated at higher altitudes than before.
The accuracy of an altimeter decreases the higher an aircraft flies. Because of this, a Vertical Separation Panel was formed in the ’50s to re-evaluate the separation minimums needed to stay safe on higher altitudes. A few years later it was decided the separation between aircraft should still be a minimum of 1000 ft but only up to a certain flight level. At FL 290 and above separation of 2000 ft was needed to ensure separation. This still applies but with a very common exception. RVSM airspace.
Let me tell you why RVSM airspace was implemented: In the late ’70s the world faced fuel shortages and the fuel costs increased as well as growing demand for air travel and a demand for more efficient use of the airspace available. During this time ICAO started to investigate the possibilities of reducing the vertical separation at FL 290 to FL 410.
After many years of evaluation and planning RVSM airspace began to be implemented in 1997. This meant aircraft with the right equipment would only need separation of 1000 ft within the airspace. This was possible because, with time, aircraft equipment had been improved. Modern aircraft have more accurate altimeters and better autopilots to help the pilots fly on the desired path. To be RVSM-compliant the aircraft need two independent primary altimeters, an automatic altitude control system, and a secondary surveillance radar transponder amongst some other certified equipment. In addition, pilots need specialized training.
If you can’t comply with this, you may need to stay below FL 290 or climb above FL 410 (while being separated by 2000 ft from other aircraft during the whole climb). In most cases that is, because there are exceptions. Sometimes state aircraft like military, customs, and police are approved to fly within RVSM-airspace without being RVSM-compliant. When doing this, they shall be separated by 2000 ft at all times. RVSM has continued to be implemented in different regions since 1997. According to Eurocontrol, all European airspace between FL 290 and FL 410 has been RVSM airspace since 2012.
In theory, flight level capacity is doubled in RVSM airspace, meaning higher air traffic capacity. Since there are more flight levels available it can help pilots fly closer to Optimum Altitude to save fuel and they have a better chance of avoiding turbulence on certain flight levels. According to ICAO, 2003, the aircraft fuel burn penalty is about 1% for every 1000 ft below optimum altitude. A quite significant penalty. The equipment and training requirements are of course there for a reason. To make sure operation within RVSM airspace is no bigger than outside the airspace.
Sounds great, right? But does a pilot really need to know about RVSM? Let me tell you a story based on a true event where the pilots actually got really good use of their RVSM-knowledge…
It was an early morning in July when Captain Tom and First officer Andrea met up at the company crew room. They were both excited to work since they had just recently come back from summer leave and they longed for going back up in the air. They quickly discovered they both had gone to Greece on vacation. Both to popular tourist destinations not far from each other. What a coincidence! They would surely have a lot to talk about during the day ahead. They went on with the planning for the coming flight. They went through the flight plan and checked the weather and agreed. It was a beautiful day with light winds and clear blue skies, “severe CAVOK” as many pilots jokingly would say about the weather on a day like this.
They met up with the cabin crew, who were also in a very good mood, and they all made their way through the airport as they small talked with each other. Andrea told Tom about her brand new car, a white mini SUV from a German brand. “Really? I have the same model to commute to work. Great car, love it!” Captain Tom responded as they approached their gate.
“Do you want to fly first or the second sector Andrea?” Captain Tom asked as they walked down the bridge towards their aircraft for the day, Andrea decided Captain Tom be pilot flying the first sector. And she would be pilot monitoring. She wanted to save the fun part of flying for later.
They went into the cockpit and checked the status of the aircraft before First Officer Andrea made her way out for the exterior inspection. She came back and informed the Captain that everything looked good on the exterior. And they went ahead with cockpit preparations. The Purser came into the flight deck to ask if it was okay to start boarding. Captain Tom gave her a smile and a thumbs up.
“Pre-flight checklist” Captain Tom commanded, and they did their checks including an altimeter check, 10 ft difference, well within limits. They continued their workflow, with several normal checklists to do. Push back, start-up, taxi, and so on and soon they finally made their way up in the air. It felt good to be back up there. Especially a beautiful morning like this when the air is calm and still has a tint of pink, orange and red from the sunrise.
“Pre-level” Captain Tom called out when they approached FL 360, their assigned flight level for now. Andrea was confused when they leveled off since her altimeter had 700 ft to go to the assigned flight level.
Sarah Mårts
As they climbed First officer Andrea made the RVSM check and the altimeter difference was still within limits. They talked about their vacations during their climb “Did you like the Greek olives Tom asked, weren’t they just so good?” Andrea agreed and thought back to sunny days with good food, blue water, and sunny skies. “Pre-level” Captain Tom called out when they approached FL 360, their assigned flight level for now. Andrea was confused when they levelled off since her altimeter had 700 ft to go to the assigned flight level. She made the captain aware of the situation. They are both good pilots and they knew it’s a good idea to cross-check the primary altimeters with the standby altimeter to find out which one most likely shows the wrong indication. Which seemed to be the first officer altimeter in this case.
An aircraft passed close by in the opposite direction when Andrea remembered about RVSM airspace. Without two independent primary altimeters, they were not RVSM compliant. So she told the Captain about her idea. “First things first Andrea, let’s consult our documents and then we make a decision on what to do” Captain Tom responded when the Purser called the flight deck to offer some coffee. They said no thanks and gave the purser a heads up they had some technical issues and promised to get back to her soon.
They consulted their checklists they realized they couldn’t fix the faulty altimeter. And the handbook indeed stated Airplane does not meet RVSM airspace requirements. So they decided to contact radar control.
“Scandleard142, unable RVSM due equipment,” she told the radar controller according to standard radio phraseology. “We have only one primary altimeter,” she added.
“Scandlearn142, descend flight level 280” the radar controller responded, and asked about their intentions.
Captain Tom and First Officer Andrea discussed what their next action should be. On FL 280 the fuel burn would be so high they would never make it to their destination. They decided they should consider an alternate and agreed the best option was to return back to their home base.
The Captain went ahead and briefed the cabin crew and the passengers about their return back to the airport they had just left. And then Captain Tom and First officer Andrea prepared for landing back at their home base. After a normal uneventful landing they were back, parked in the same gate they had just left.
“We did a good job up there Andrea, what a start to the day.” Captain Tom said as they both smiled at each other, happy to have made it back to the ground without further surprises “Let’s call the technicians and see if they can fix this so we can give it another go on flying our passengers to their destination. “Even if they will be late our number one priority is of course their safety.“
This was a day with complications but without drama. Like it usually is when technical issues are encountered. But that’s assuming the crew is well trained. In terms of vertical separation, knowing what you need to be RVSM-compliant is important so that you, as a pilot, can make sure you are flying your passengers safely to their destination. And can you believe it, The Captain and First Officer had similar food preferences, travel interests, and even the same cars. Only their altimeters did not match.