diff --git a/src/traffic/algorithms/filters/consistency.py b/src/traffic/algorithms/filters/consistency.py
new file mode 100644
index 00000000..46062164
--- /dev/null
+++ b/src/traffic/algorithms/filters/consistency.py
@@ -0,0 +1,348 @@
+from __future__ import annotations
+
+import operator
+import warnings
+from typing import Any, ClassVar
+
+import numpy as np
+import numpy.typing as npt
+import pandas as pd
+
+from . import FilterBase
+
+NM2METER = 1852
+
+
+def distance(
+    lat1: npt.NDArray[np.float64],
+    lon1: npt.NDArray[np.float64],
+    lat2: npt.NDArray[np.float64],
+    lon2: npt.NDArray[np.float64],
+) -> npt.NDArray[np.float64]:
+    r = 6371000
+    phi1 = lat1
+    phi2 = lat2
+    delta_phi = lat2 - lat1
+    delta_lambda = lon2 - lon1
+    a = (
+        np.sin(delta_phi / 2) ** 2
+        + np.cos(phi1) * np.cos(phi2) * np.sin(delta_lambda / 2) ** 2
+    )
+    res = r * (2 * np.arctan2(np.sqrt(a), np.sqrt(1 - a)))
+    return res / NM2METER  # type: ignore
+
+
+def lag(horizon: int, v: npt.NDArray[np.float64]) -> npt.NDArray[np.float64]:
+    res = np.empty((horizon, v.shape[0]))
+    res.fill(np.nan)
+    for i in range(horizon):
+        res[i, : v.shape[0] - i] = v[i:]
+    return res
+
+
+def diffangle(
+    a: npt.NDArray[np.float64], b: npt.NDArray[np.float64]
+) -> npt.NDArray[np.float64]:
+    d = a - b
+    return d + 2 * np.pi * (  # type: ignore
+        (d < -np.pi).astype(float) - (d >= np.pi).astype(float)
+    )
+
+
+def dxdy_from_dlat_dlon(
+    lat_rad: npt.NDArray[np.float64],
+    lon_rad: npt.NDArray[np.float64],
+    dlat: npt.NDArray[np.float64],
+    dlon: npt.NDArray[np.float64],
+) -> tuple[npt.NDArray[np.float64], npt.NDArray[np.float64]]:
+    a = 6378137
+    b = 6356752.314245
+    e2 = 1 - (b / a) ** 2
+    sinmu2 = np.sin(lat_rad) ** 2
+    rm = a * (1 - e2) / (1 - e2 * sinmu2) ** (3 / 2)
+    bign = a / np.sqrt(1 - e2 * sinmu2)
+    dx = dlon * bign * np.cos(lat_rad)
+    dy = dlat * rm
+    return dx, dy
+
+
+def compute_gtgraph(dd: npt.NDArray[Any]) -> Any:
+    """compute the graph of points complying with the speed limits: i and j are
+    adjacent if i can be reached by j within the speed limits"""
+
+    import graph_tool as gt
+
+    n = dd.shape[1]
+    # horizon = dd.shape[0]
+    g = gt.Graph(g=n, directed=True)  # ,g=dd.shape[0])
+    eprop_dist = g.new_edge_property("int")
+    d = {i: v for i, v in enumerate(g.vertices())}
+    edges = [(i, i + h) for h, i in zip(*np.nonzero(dd)) if h > 0]
+    g.add_edge_list(edges)  # ,eprops=eprop_dist)
+    eprop_dist = g.new_edge_property("int", val=-1)
+    return d, g, eprop_dist
+
+
+def get_gtlongest(dd: npt.NDArray[Any]) -> Any:
+    """compute the longest path of points complying with the speed limits"""
+    # import graph_tool as gt
+    import graph_tool as gt
+
+    v, g, prop_dist = compute_gtgraph(dd)
+    # n = g.num_vertices()
+    vend = g.add_vertex()
+    vstart = g.add_vertex()
+    for v in g.iter_vertices():
+        if v != vend:
+            e = g.add_edge(v, vend)
+            prop_dist[e] = -1
+        if v != vstart:
+            e = g.add_edge(vstart, v)
+            prop_dist[e] = -1
+    longest_path, _ = gt.topology.shortest_path(
+        g,
+        source=vstart,
+        target=vend,
+        weights=prop_dist,
+        negative_weights=True,
+        dag=True,
+    )
+    longest_path = list(map(int, longest_path))
+    return longest_path
+
+
+def get_nxlongest(dd: npt.NDArray[Any]) -> Any:
+    import networkx as nx
+
+    n = dd.shape[1]
+    g = nx.DiGraph()
+    for i in range(n):
+        g.add_node(i)
+    edges = [
+        (i, i + h, {"weight": -1}) for h, i in zip(*np.nonzero(dd)) if h > 0
+    ]
+    g.add_edges_from(edges)
+    for i in range(n + 1):
+        g.add_edge(-1, i, weight=-1)
+    for i in range(-1, n):
+        g.add_edge(i, n, weight=-1)
+    path = nx.shortest_path(
+        g, source=-1, target=n, weight="weight", method="bellman-ford"
+    )
+    return path
+
+
+def exact_solver(dd: npt.NDArray[Any]) -> npt.NDArray[np.bool_]:
+    try:
+        longest_path = get_gtlongest(dd)  # ,weights)
+    except ImportError:
+        warnings.warn(
+            "graph-tool library not installed, "
+            "switching to slower NetworkX library"
+        )
+        longest_path = get_nxlongest(dd)
+    res = np.full(dd.shape[1], True)
+    res[np.array(longest_path)[1:-1]] = False
+    return res
+
+
+def approx_solver(dd: npt.NDArray[Any]) -> npt.NDArray[np.bool_]:
+    ddbwd = np.empty_like(dd)
+    ddbwd.fill(False)
+    for h in range(dd.shape[0]):
+        assert dd[h, : dd.shape[1] - h].shape == ddbwd[h, h:].shape
+        ddbwd[h, h:] = dd[h, : dd.shape[1] - h]
+    res = np.full(dd.shape[1], True)
+    out = 10 * res.shape[0]  # 30000
+
+    def selectpoints(iinit, dd, opadd, argmaxopadd):  # type: ignore
+        jumpmin = dd[1:].argmax(axis=0) + 1
+        jumpmin[(~dd[1:,]).all(axis=0)] = out
+        ### computes heuristic
+        succeed = np.zeros(res.shape, dtype=np.int64)
+        nsteps = 10
+        posjumpmin = np.arange(res.shape[0])
+
+        def check_in(posjumpmin: Any) -> npt.NDArray[np.bool_]:
+            return np.logical_and(  # type: ignore
+                0 <= posjumpmin,
+                posjumpmin < res.shape[0],
+            )
+
+        for k in range(nsteps):
+            valid = check_in(posjumpmin)
+            posjumpminvalid = posjumpmin[valid]
+            posjumpmin[valid] = opadd(posjumpminvalid, jumpmin[posjumpminvalid])
+            succeed[check_in(posjumpmin)] += 1
+        posjumpmin[succeed != nsteps] = opadd(
+            0, out - succeed[succeed != nsteps]
+        )
+
+        #### end compute heuristic
+        def selectjump(
+            i: int,
+            cjump: npt.NDArray[np.int64],
+            prediction: npt.NDArray[np.int64],
+        ) -> int:
+            return cjump[argmaxopadd(prediction[opadd(i, cjump)])]  # type: ignore
+
+        i = iinit
+        while 0 <= i < res.shape[0]:
+            res[i] = False
+            candidatejump = np.arange(1, dd.shape[0])[dd[1:, i]]
+            if len(candidatejump) == 0:
+                break
+            else:
+                i = opadd(i, selectjump(i, candidatejump, posjumpmin))
+
+    ss = np.sum(dd[1:], axis=0) + np.sum(ddbwd[1:], axis=0)
+    iinit = ss.argmax()
+    selectpoints(iinit, dd, operator.add, np.argmin)  # type: ignore
+    selectpoints(iinit, ddbwd, operator.sub, np.argmax)  # type: ignore
+    return res
+
+
+def consistency_solver(
+    dd: npt.NDArray[Any], exact_when_kept_below: float
+) -> npt.NDArray[np.bool_]:
+    if exact_when_kept_below == 1:
+        return exact_solver(dd)
+    else:
+        mask = approx_solver(dd)
+        if 1 - np.mean(mask) < exact_when_kept_below:
+            return exact_solver(dd)
+        else:
+            return mask
+
+
+class FilterConsistency(FilterBase):
+    """
+    Filters noisy values, keeping only values consistent with each other.
+    Consistencies are checked between points :math:`i` and points :math:`j \\in
+    [|i+1;i+horizon|]`. Using these consistencies, a graph is built: if
+    :math:`i` and :math:`j` are consistent, an edge :math:`(i,j)` is added to
+    the graph. The kept values is the longest path in this graph, resulting in a
+    sequence of consistent values.  The consistencies checked vertically between
+    :math:`t_i<t_j` are:: :math:`|(alt_j-alt_i)-(t_j-t_i)* ROCD_i| <
+    clip((t_j-t_i)*dalt_dt,dalt_min,dalt_max)` and
+    :math:`|(alt_j-alt_i)-(t_j-t_i)* ROCD_j| <
+    clip((t_j-t_i)*dalt_dt,dalt_min,dalt_max)` where :math:`dalt_dt`,
+    :math:`dalt_min` and :math:`dalt_max` are thresholds that can be specified
+    by the user.
+
+    The consistencies checked horizontally between :math:`t_i<t_j` are:
+    :math:`|track_i-atan2(lat_j-lat_i,lon_j-lon_i)| < (t_j-t_i)*dtrack_dt` and
+    :math:`|track_j-atan2(lat_j-lat_i,lon_j-lon_i)| < (t_j-t_i)*dtrack_dt` and
+    :math:`|dist(lat_j,lat_i,lon_j,lon_i)-groundspeed_i*(t_j-t_i)| <
+    clip((t_j-t_i)*groundspeed_i*ddist_dt_over_gspeed,0,ddist_max)` where
+    :math:`dtrack_dt`, :math:`ddist_dt_over_gspeed` and :math:`ddist_max`
+    are thresholds that can be specified by the user.
+
+    If :math:`horiz_and_verti_together=False` then two graphs are built, one
+    for the vertical variables and one for horizontal variables. Otherwise, only
+    one graph is built. Using two graphs is more precise but slower.  In order
+    to compute the longest path faster, a greedy algorithm is used. However, if
+    the ratio of kept points is inferior to :math:`exact_when_kept_below`
+    then an exact and slower computation is triggered. This computation uses the
+    Network library or the faster graph-tool library if available.
+
+    This filter replaces unacceptable values with NaNs. Then, a strategy may be
+    applied to fill the NaN values, by default a forward/backward fill. Other
+    strategies may be passed, for instance do nothing: None; or interpolate:
+    lambda x: x.interpolate(limit_area='inside')
+
+    """
+
+    default: ClassVar[dict[str, float | tuple[float, ...]]] = dict(
+        dtrack_dt=2,  # [degree/s]
+        dalt_dt=200,  # [feet/min]
+        dalt_min=50,  # [feet]
+        dalt_max=4000,  # [feet]
+        ddist_dt_over_gspeed=0.2,  # [-]
+        ddist_max=3,  # [NM]
+    )
+
+    def __init__(
+        self,
+        horizon: int | None = 200,
+        horiz_and_verti_together: bool = False,
+        exact_when_kept_below: float = 0.5,
+        **kwargs: float | tuple[float, ...],
+    ) -> None:
+        self.horiz_and_verti_together = horiz_and_verti_together
+        self.horizon = horizon
+        self.thresholds = {**self.default, **kwargs}
+        self.exact_when_kept_below = exact_when_kept_below
+
+    def apply(self, data: pd.DataFrame) -> pd.DataFrame:
+        lat = data.latitude.values
+        lon = data.longitude.values
+        alt = data.altitude.values
+        rocd = data.vertical_rate.values
+        gspeed = data.groundspeed.values
+        t = (
+            (data.timestamp - data.timestamp.iloc[0])
+            / pd.to_timedelta(1, unit="s")
+        ).values
+        assert t.min() >= 0
+        n = lat.shape[0]
+        horizon = n if self.horizon is None else min(self.horizon, n)
+
+        def lagh(v: npt.NDArray[np.float64]) -> npt.NDArray[np.float64]:
+            return lag(horizon, v)
+
+        dt = abs(lagh(t) - t) / 3600
+        lat_rad = np.radians(lat)
+        lon_rad = np.radians(lon)
+        lag_lat_rad = lagh(lat_rad)
+        # mask_nan = np.isnan(lag_lat_rad)
+        dlat = lag_lat_rad - lat_rad
+        dlon = lagh(lon_rad) - lon_rad
+        dx, dy = dxdy_from_dlat_dlon(lat_rad, lon_rad, dlat, dlon)
+        track_rad = np.radians(data.track.values)
+        lag_track_rad = lagh(track_rad)
+        mytrack_rad = np.arctan2(-dx, -dy) + np.pi
+        thresh_track = np.radians(self.thresholds["dtrack_dt"]) * 3600 * dt
+        ddtrack_fwd = np.abs(diffangle(mytrack_rad, track_rad)) < thresh_track
+        ddtrack_bwd = (
+            np.abs(diffangle(mytrack_rad, lag_track_rad)) < thresh_track
+        )
+        ddtrack = np.logical_and(ddtrack_fwd, ddtrack_bwd)
+        dist = distance(lag_lat_rad, lagh(lon_rad), lat_rad, lon_rad)
+        absdist = abs(dist)
+        gdist_matrix = gspeed * dt
+        ddspeed = np.abs(gdist_matrix - absdist) < np.clip(
+            self.thresholds["ddist_dt_over_gspeed"] * gspeed * dt,
+            0,
+            self.thresholds["ddist_max"],
+        )
+        ddhorizontal = np.logical_and(ddtrack, ddspeed)
+
+        dalt = lagh(alt) - alt
+        thresh_alt = np.clip(
+            self.thresholds["dalt_dt"] * 60 * dt,
+            self.thresholds["dalt_min"],
+            self.thresholds["dalt_max"],
+        )
+        ddvertical = np.logical_and(
+            np.abs(dalt - rocd * dt * 60) < thresh_alt,
+            np.abs(dalt - lagh(rocd) * dt * 60) < thresh_alt,
+        )
+        if self.horiz_and_verti_together:
+            mask_horiz = consistency_solver(
+                np.logical_and(ddhorizontal, ddvertical),
+                self.exact_when_kept_below,
+            )
+            mask_verti = mask_horiz
+        else:
+            mask_horiz = consistency_solver(
+                ddhorizontal, self.exact_when_kept_below
+            )
+            mask_verti = consistency_solver(
+                ddvertical, self.exact_when_kept_below
+            )
+        data.loc[
+            mask_horiz, ["track", "longitude", "latitude", "groundspeed"]
+        ] = np.nan
+        data.loc[mask_verti, ["altitude", "vertical_rate"]] = np.nan
+        return data
diff --git a/src/traffic/data/samples/__init__.py b/src/traffic/data/samples/__init__.py
index edcda6e4..173eaaba 100644
--- a/src/traffic/data/samples/__init__.py
+++ b/src/traffic/data/samples/__init__.py
@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import types
-from datetime import timezone
 from functools import lru_cache
 from pathlib import Path
 from typing import Any, Union, cast
@@ -47,7 +46,7 @@ def get_flight(filename: str, directory: Path) -> Flight | Traffic:
                 df.last_position * 1e6
             ).dt.tz_localize("utc")
         )
-    if flight.data.timestamp.dtype.tz != timezone.utc:
+    if not hasattr(flight.data.timestamp.dtype, "tz"):
         flight = flight.assign(
             timestamp=lambda df: df.timestamp.dt.tz_localize("utc")
         )