The HASEL check is a safety checklist to help keep aviation safe. It stands for Height, Area, Security/Safety, Engine, Lookout. The acronym HASEL is used as a mnemonic to help pilots remember the checklist without having to rely on a physical checklist.
From a flight training perspective, this safety check needs to be completed prior to performing any “S” exercises. This would include slow flight, stalls, spins, spiral dives, steep turns, and any other unusual flight attitudes.
2000’ AGL is the required minimum. Why 2000’ AGL? Look up 602.27 in the CARs. More altitude equals more time to recover. Even if you’re able to hold the altitude perfectly during slow flight, is it really a good idea to do it 300’ off the ground? 2000’ AGL also includes the recovery from the manoeuvre so it’s suggested to start the exercise at 3000’ AGL. Some exercises may require more altitude to recover, such as spins and spiral dives. Check with your instructor and POH. That said, the POH may suggest or require a different minimum altitude depending on the manoeuvre. If the altitude is different than CARs, go with the higher one.
The height that we’re referring to is above ground level (AGL). The altimeter displays above sea level (ASL), assuming the altimeter setting is correct. You’ll need to know the ground elevation in order to figure out how much to add to get the altitude for reference while in the plane. A quick way is to look for towers or obstacles in your area. The tower will have two numbers associated with it. A number with brackets indicate the top of the tower in ASL; and the number without brackets indicate the height of the tower. Find the difference of the two numbers to get the ground elevation. You can practice with the image above. Use the tower just south of Keswick with numbers “(1052)” and “247”. The difference of the two numbers is 805. Therefore, the ground elevation of that tower is 805’. Compare different towers in the area to get an average in your area.
Now that you figured out the minimum altitude to recover and start the exercise at, in what situation would you be unable to achieve that minimum? According to 602.115 in the CARs, you have to be at least 500’ vertically from cloud. Depending on the cloud ceilings, there could be days (or weeks) where the clouds are too low to practice upper airwork.
Make sure that you won’t be over any built-up areas during your manoeuvre. This is in case something happens, casualties will be minimized. Generally, built up areas are where buildings are side-by-side much like towns and cities. Plan ahead as the area will be dependent on what type of lookout you’ll do.
Check the cockpit and cabin for any loose objects and secure them. Any maps, pens, clipboards, checklist, etc can be a potential projectile. Better safe than sorry! Don’t forget this includes all occupants so check seats and seat belts of yourself and your instructor.
You want the engine to be responsive and predictable so make sure it’s within parameters. A simple way is to do the pre-landing checks (or downwind checks). It’ll be slightly different depending on the aircraft and pilot, but most would generally follow a geographic flow going from left to right.
Items to check would be: primer locked, master on, mags on both, switches as required, carb heat as required, fuel pump as required, mixture rich, fuel selector both, fuel quantity ok, T+P (oil temperature and pressure) in the green.
Scan the sky for other traffic. Other planes might be nearby and you just missed their radio call (or they didn’t make one). Look all around you including above and below. The design of your aircraft will restrict your view (high-wing vs low-wing, number of windows and its design and location, etc). To solve this issue, perform a lookout while doing an 180° heading change. The banked wings in addition to the turn(s) would allow you to scan more of the sky. Limit the bank angle to <30°. The objective is to focus on scanning for traffic, not focusing on executing a steep turn. It’s generally accepted to perform a single 180° turn or a 90° turn one way and then another 90° the other way. This step is intertwined with the ‘Area’ check part of HASEL. Plan ahead and determine where you’ll be after performing the lookout, and use the one 180° or the two 90° turn to avoid executing your aerobatic manoeuvre above built-up areas. A full 360° clearing turn is another option, but it’s usually used when the area is busy. In that situation, it might better to go somewhere else instead.
Remember, the HASEL check is to help keep you and others safe. Don’t rush through the checks just to save time. It needs to be done prior the exercise. Even if you do slow flight followed by stalls and then spiral dives back-to-back, you’ll have to do two other HASEL checks in between those exercises. Your position will be different, other aircraft’s position and/or altitude will be different, your aircraft condition might have changed, etc.